It was posted like some kind of gotcha but....this book was in the dataset.
I'm aware that LLMs don't keep the dataset in memory but it "knows" that this is an existing work but these sites aren't doing any wild calculations to figure out if it was AI-generated. They basically just check to see if the sentences exist elsewhere and they do. In the original dataset.
So it was wrong to say it's AI-generated but it correctly identified that it's not original.