Opamañño in pāli would be Aupamanyavaḥ in Sanskrit (the final -o is a contraction of -avaḥ), and the initial o = Skt. ‘au’. Upamanyu(ḥ) would have to be the ancestor of an Aupamanyava(ḥ). This confusion between the masculine nominative singular ending -o (for -a ending stems) where Sanskrit has -aḥ and a virtually identical ‘o’ in Pāli which is a contraction of ‘ava’ in Sanskrit led to a misinterpretation in Pāli of the word opamañño as being = *aupamanyaḥ therefore leading to a confused instrumental form opamaññena (“brāhmaṇena pokkharasātinā opamaññena subhagavanikena” in MN99) when it should have been opamaññavena (like māṇava → māṇavena). However at another place the declension of a -u ending name’s derivative is correctly identified – “atha kho kāpilavatthavā sakyā yena bhagavā tenupasaṅkamiṃsu”.
He is well known in late-vedic texts dated to the time of the Buddha, such as the Taittirīya-prātiśākhya (a phonological & grammatical text describing the pronounciation & grammatical peculiarities of the Sanskrit dialects used in the Taittirīya-saṃhitā of the Kṛṣṇa-Yajurveda), where some of his opinions on the topic are quoted by name - as he is recognized there to be an authority on Sanskrit grammar)
- “vyañjanaparaḥ pauṣkarasāder na pūrvaśca ñakāram”
- “prathama-pūrvo hakāraś caturthaṃ tasya sasthānaṃ plākṣi-kauṇḍinya-gautama-pauṣkarasādīnām”
- “pr̥ktasvarātparo lo ḍaṃ pauṣkarasādeḥ”
- “lavakārapūrvasparśaś ca pauṣkarasādeḥ”
- “svāravikramayor dr̥ḍhaprayatnataraḥ pauṣkarasādeḥ”
The same text also mentions a phonological observation of another scholar named Vālmīki (“pakārapūrvaś ca vālmīkeḥ” - to whom the authorship of the Sanskrit epic Rāmāyaṇa is attributed by tradition.
Writing a century or so later (in the time of the Mauryan emperor Aśoka i.e. in the 3rd century BCE), the grammarian Kātyāyana (while commenting on the grammatical sūtras of Pāṇini) records another grammatical opinion of the scholar Pauṣkarasādi “cayaḥ dvitīyāḥ śari pauṣkarasādeḥ”. Kātyāyana also mentions Aśoka’s regnal title Devānāmpriyaḥ as an exception to one of the sūtras of Pāṇini, and elsewhere calls him a vegetarian king (śaka-pārthivaḥ). Another grammarian Patañjali, writing a century after Kātyāyana (i.e. in the 2nd century BCE, further adds that Pauṣkarasādi was an ācārya, not just a scholar in his own right but a teacher, presumably in the grammatical tradition.
Pauṣkarasādi is also mentioned in the Śāṅkhāyana-Āraṇyaka in connection with his opinions on ṚgVedic ritual.
Going by these references, Pauṣkarasādi must have lived in the late 5th century and/or the early 4th century BCE. His name indicates he was the son of a ‘Puṣkarasad’ (“a person who was settled in Puṣkara” - presumably Puṣkarāvati/Puṣkalāvati, a prominent city in the northwestern Indian province of Gandhāra, mentioned as Peucelaotis in Greek records connected to Alexander’s invasion of Gandhāra around 325 BCE).
Not just Pauṣkarasādi, there are many other names in the early buddhist texts that (by restoration to their Sanskrit equivalents) be traced in coeval Sanskrit texts. Names such as Tārukṣya (Pāli: Tārukkha); Taudeya (Pāli: Todeyya), a name whose grammatical derivation is mentioned by the 4th century BCE grammarian Pāṇini as being from the name of their village Tudī; Jānaśruti (Pāli: Jānussoṇi); etc. Several other names (when restored) are independently verifiable in coeval texts written in Sanskrit.
The commentary invents reasons like these for a huge number of other things, and many of those reasons are not credible (unless they are independently verifiable). So I dont normally rely on Pāli commentarial speculations unless there is independent evidence in support of the same. For example commentary on MN3 says “tudigāmo nāma atthi, tassa adhipatittā todeyyoti saṅkhyaṃ gato” (which is traceable to Pāṇini’s sutra 4.3.94 tūdīśalāturavarmatīkūcavārāt ḍhakchaṇḍhañyakaḥ where the grammatical derivation of the name Taudeya from the name of the Tudī grāma, is explained in detail) - the MN3 commentary is wrong in quoting the name tudi with a short vowel ‘i’, the nominal-derivative suffix eya applies to feminine names, so the name should end with a long vowel ‘ī’.
The Dhammacariya-sutta in question appears to have been originally titled Kapila-suttam, but which was (when it was subsequently noticed to be the personal name that must not be uttered) presumably subsequently renamed to Dhammacariya-suttam (dhammacariya being the first word of the sutta), this change must have happened when the historical Buddha’s personal name was still in living memory - this sutta being a particularly early one, being located in the Sutta Nipata. Due to perhaps being accidentally preserved in another redaction, both names of this sutta happen to have been preserved until today. Very few suttas are preserved with alternative names in this way, and none else that I can remember immediately.
The name Kapila as the name of a place is also found in some non-Buddhist Sanskrit texts, and even in the Buddhacarita of Aśvaghoṣa - “iti narapatiputrajanmavṛddhyā sajanapadaṃ kapilāhvayaṃ puraṃ tat”
Why the city is called Kapilavāstu (home of Kapila) in the early Buddhist texts - rather than Kapila itself (which is independently found attested in the non-EBT texts) may have been to not confuse the name of the city with the name of the Buddha himself, so they may have added the suffix -vāstu to the name to show that the reference was to a place and not to the person of the same name (where the name was a name that would be immediately recognized when heard, and hence liable to confusion). The name Kapilavāstu is not to be met with in any external (non-Buddhist) early texts, but the name Kapila is attested as a place name, so the addition of -vāstu appears to be an innovation internal the authors of the EBT canonization committee.
Can you please cite the place where this is found - as that would be very odd. Malla is the name of a janapada (country). There may have been Mallas residing in a particular place within the Malla janapada who were known to the Buddha because they may have previously introduced themselves to the Buddha when they earlier attended a discourse - and who would have self-introduced themselves to him on arrival by mentioning their gotra names via the customary abhivādana (traditional self-introduction custom) – as the common refrain goes in hundreds of suttas “…abhivādetvā ekamantaṃ nisīdi…”
So the Buddha may have been made aware of the gotras of a certain previously known-group of Mallas as a result of their prior self-introduction, that wouldnt necessarily lead to the inference that all other Mallas belonged to the Vāsiṣṭha-gotra. It may have simply meant that the Buddha had prior reason to believe that those attending that particular discourse were people from a specific place in the Malla janapada and were known to be Vāsiṣṭhas by prior introduction.
