Nothing is being copied. If you understand how AI models work you'd realize that's impossible considering the model is a few GB. How could every piece of artwork be in there? It's not a database lookup.
But can you seriously deny that everything the model generates is a derivative of the inputs? And if it's a derived work, it might not constitute "fair use" of the input materials. That depends on.... well, I'm not a copyright lawyer, so I won't attempt to specify, but I don't think we have any clear answers yet.
Everything is a derivative of everything. What is art school? They derive their skills from other well known artists.