Using pixel-space or latent-space distances to measure if a generative model has simply memorized the training data is a common evaluation metric in ML literature. If the website is using the full training set of LAION 5-B used to train Stable Diffusion, then I find it extremely convincing that SD has generalized to the data distribution it was trained on, and does not simply regurgitate other people's artwork. If there is a way to find more similar images, I have yet to see it.

I think this website is evidence SD is a novel image generator, and rarely creates infringing images (at least in the way we thought of infringing before these kinds of AI).