Let’s say I read Harry Potter, and decide to use stylistic cues from that book to write my own kid fiction best seller. Is that bad?
I may be able to recite text from Harry Potter verbatim; in fact I can: “fancy seeing you here, professor mcgonagall”. That’s from the first chapter of the first book I think. Obviously I shouldn’t use that in my book, but the fact that I can recite it doesn’t prove I did a plagiarism. Even having all of JK’s works memorized would not be evidence.
So when a LLM does the same thing, I think that’s the sort of test that will come up in court. Whether a human would be guilty of plagiarism having done the same thing. And the answer will be no, because it IS a human using a tool.