Essentially they want a copyright on knowledge, Such a law can be misused. Also its hard to prove this just by looking at the weights, and for something as large as GPT-3.5 it would not be easy to prove this.
You’re right. Knowledge provided by authors isn’t unique and as long as AI doesn’t literally cite complete chapters word for word, this doesn’t seem to have anything to do with copyright.
To be fair though its an Open secret they trained it on Common crawl G4 and Pile databases. But proving it is another thing. By the time someone develops tooling to prove such things we will have an explainable AI.