Bhikkhu Bodhi’s Connected Discourses of the Buddha includes extensive discussions of variant readings, as well as summaries of the commentary. I don’t replicate these here, but usually I follow Bodhi’s readings and note where I differ.

“Deity” is devatā, which in Pali as in English is an abstract noun. Though feminine in grammatical gender, it does not imply that the deity is female. Here, for example, the deity is addressed with the masculine form āvuso.

“Good fellow” (mārisa; Sanskrit mārṣa, māriṣa) is a special term of address used by deities and sometimes by kings. The term harks back to Sanskrit mādṛśa, “one like me”, in the sense of having a comparable status, i.e. “fellow”. | The Buddha lived and taught in the Gangetic plain, a region characterized by deadly and unpredictable flooding.

That āyūhati means “swim” is clear from SN 2.5:3.5.

The deity’s counter-question shows that the Buddha’s answer was deliberately obscure.

The teaching suggests a state of poised flow, where one is neither stuck in attachments, nor restlessly straining to get somewhere else.