Of the three claims you just made, two are clearly false and the third is probably also...

You can prove something is created by AI by e.g. showing the transcripts, especially from the vendor side.

You cannot prove that something isn't created with AI, at least not if you require incontrovertible proof (outside of, like, working in some kind of verifiably AI-free clean room, or doing something that current models are provably unable to demonstrate). But you certainly might be able to prove it to the satisfaction of the legal system.

If AI generated content cannot be copyrighted, it does not follow at all that they can't infringe copyright; there is no deductive step there that I can think of.