Well, I am not exactly a hotshot 8086 programmer (though I do alright) but if I was asked to reproduce the IBM BIOS (which I have seen) I think I would come up with something very similar but not identical - it is really not rocket science code, so the LLM replacing me would have rather few alternatives to choose from.
I believe those are actually separate matters. A proper clean room implementation on the one hand, and the question of whether or not a particular outcome was a foregone conclusion on the other. I don't recall where I saw the latter but it might have come up during Google v Oracle?