> What data and models were used to synthesize these predictions?
You have to ask the creator of ArtBreeder (https://www.artbreeder.com/about) which apparently uses BigGAN, StyleGAN, etc., trained on different datasets to offer these options:
https://i.imgur.com/5jTNgXl.jpg
That being said, there is a heavy manual touch (based on "Photoshop and historical references"). See for instance how different Septimus can appear compared to the webpage: