Since a Google product output the result, it had access to the same knowledge base as Google itself - Search, Scholar, etc. And use of copyrighted data for research purposes has always been, as far as I know, considered fair use in AI training.

Unfortunately, even if we wanted to, it might be impossible to attribute this success to the authors that it built upon.

>outside the public domain

public domain is a legal term meaning something like "free from copyright or license restrictions"

I believe in this thread people mean not that but "published and likely part of the training corpus"