That serves as evidence that the model has seen the material, and the only way the model could have seen the material is if it was pirated.

You're missing the bigger picture[1]:

  Numerous questions of law or fact common to each Class arise from Defendants’ conduct:
    whether ChatGPT itself is an infringing derivative work based on Plaintiffs’ copyrighted books;
    whether the text outputs of ChatGPT are infringing derivative works based on Plaintiffs’ copyrighted books;

It's not a simple case of "you used our copyrighted materials", it's "you're infringing on our copyright by producing works derived from materials that you used."

1. https://llmlitigation.com/pdf/03223/tremblay-openai-complain...

That assumption is the reason why it's a shady argument for infringement. There's other ways to get a summary of a book than reading it, like asking a friend who's read it to give a summary