I agree with what you wrote about the jhanas, however I’d say he wasn’t “beyond any…plane of existence” because he was still in the human realm (bhava) – no matter what his perceptions were or were not.
Yes, and this boundless, luminous all around are descriptions used to refer to some jhana states and particularly the 2nd formless attainment.
As in SN28.6:
““Reverend, going totally beyond the dimension of infinite space, aware that ‘consciousness is infinite’, I entered and remained in the dimension of infinite consciousness. …” …
“idhāhaṁ, āvuso, sabbaso ākāsānañcāyatanaṁ samatikkamma anantaṁ viññāṇanti viññāṇañcāyatanaṁ upasampajja viharāmi …pe…”
Regarding
See
and
Ven. Thanissaro sees it as a kind of consciousness beyond time and space and relates it to nibbāna, yet there are significant differences expressed in these essays.