Is it true then that if someone stole an entire code base from a vibe coded app from a non permissively licensed project and that person claimed that it was derived from an LLM and was not stolen at all that the person who stole the code is not a thief because it came from the same place? Or are they a thief because someone else copyrighted it? How do vibe coders protect themselves not knowing who else has the same derivative code or who holds the copyright first? Or can't they?

The only thing a vibe coder should be able to copyright, is the prompt text they wrote. Not the output of the LLM, only the text they wrote to instruct the LLM what to do. And even that is pretty iffy, because most of it like "put a button on a page" is not copyright-able.