That's what discovery will be for, the complaint alleges that the likely source was libgen. Most of these authors haven't released DRM-free ebooks, and it seems unlikely that OpenAI has a large scale book scanning effort (and even if they did, that authors would likely claim that to be infringement itself.)
What if it never accessed the book, but read everything relevant like episode summaries, fan wikis, and forum discussions? It would still be as conversant. Is it still infringement?