I'm not sure if "plagiarism" is the right word or not, but given that the output of an AI seems to be considered non-copyrightable*, and given also that a lot of people are very upset about generative AI being immoral**, I think it's important to identify which contributions are from the tools whose use may cause problems.

* I am not a lawyer, I'm going by articles talking about this

** I think the phrases are "copyright washing" and "plagiarism machines", amongst others