Well that’s interesting and strange to see such a difference. I was curious so I did a bit of search on DSBC, and found a few examples that may be relevant, including a Sanskrit parallel of that line.
Evaṁ kho, ānanda, bhikkhu attadīpo viharati attasaraṇo anaññasaraṇo, dhammadīpo dhammasaraṇo anaññasaraṇo.
Mahāyāna Mahāparinirvāṇa Sūtram
evaṃ hi bhikṣur ātmadvīpo bhavaty ātmaśaraṇo dharmadvīpo dharmaśaraṇo 'nanyadvīpo 'nanyaśaraṇaḥ |
This seems to agree with the common interpretation of the Pali.
Śīlapāramitāyāmanarthavarjanaṃ Pañcamaḥ Paricchedaḥ
tatra jambūdvīpaḥ pūritaḥ syādvaiyāpṛtyakarairbodhisattvaiḥ |
jambūdīpapramāṇaiścoddeśasvādhyāyābhiyuktairbodhisattvairekasya pratisaṃlapanābhiyuktasya bodhisattvasyopasthānaparicaryā kartavyā |
It uses both dvīpa and dīpa as part of Jambudvipa?
yathā candrapradīpasūtre kāyasaṃvaramadhye paṭhayate-na hastalolupo bhavati na pādalolupaḥ hastapādasaṃyata iti ||
bodhicittavimalāgnisuprabhaṃ dharmadīpa samujvālayiṣyati ||
Here is dharmadīpa. But in this line, it seems to be connected to fire and light.
Maybe an original double meaning of both seclusion (island), and dhyana / samadhi (light)?