So? Humans aren't copyrightable works. But a bunch of weights that constitutes the model is just data, and that data can very well contain copyrighted works. The question is whether it does in any meaningful sense. And if it can reproduce them verbatim with the right prompt, I don't see how the answer could be "no", anymore so than a password-protected archive of a copyrighted JPEG.
There's a specific prompt which makes a human artist produce such an image without img2img too: "Please draw the Mona Lisa". There - you just did it in your head while reading this comment!