But the Abyss mode looks almost identical to krillion - from the very concept of trying to guess rare answers, to the nautical diving theme, down to the almost-pixel-art style..?

It's incredible to suggest that this wasn't based on either Krillion, or that both games were based on something else.

(To be clear, I'm not accusing you of explicitly lifting the concept - but that's the problem with using AI to generate too much, it'll obviously re-use what it's seen before.)

edit: actually, you say "A large part of the code was written with AI tools, but the artistic direction the concept and every choice design are human-made" - it's just wildly improbable for the two to look and feel so similar.

The UI and graphics are 100% just a reskin of Krillion...