You're jumping to a conclusion that the data doesn't warrant, I suspect because it's a conclusion that suits you.
They're doing something like a "reverse image search" from an AI generated image over the original dataset and returning a few examples that have a high degree of similarity. There's no guarantee that the images they return are actually the ones combined to create the AI image. In fact their results are dubious - see Saurik's comment:
https://news.ycombinator.com/item?id=34671149
I don't have an opinion regarding the question of whether SD creates art or not. To be honest, as someone who enjoys art or kind-of-art in many forms, it's not important to me (although, of course, I can see why it is important to someone who makes a living from art or AI generated images).
However, this website doesn't add anything except noise to either side of the debate, from what I can see.