If you're an author with a book likely to have be hoovered up, I wonder what you'd get from the fb models if you asked "complete this in the style of [author] in [book]: [quite a long excerpt]" If you get a direct quote then you're good with your claim, surely.
Whatever the ruling one thing is for sure, plagiarism is no longer the sincerest form of flattery. The human authors are out for AI blood on this.