If you click "Edit Genes" (e.g. on the upper-right of https://artbreeder.com/i?k=755521d9fe07456286a06f06) you'll find a bunch of sliders. StyleGAN uses sliders like this to control various facial features. For any given StyleGAN model, you can find a slider for a given attribute as follows: Create a classifier for that attribute (for example, "blond hair" probability), generate 50,000 or so outputs from the model, classify each image, then plot a fitted line through all 50k latents. You now have a blonde hair slider for your specific model.

Ok, but sliders aren't unique to nVidia's licensed model. How do we check?

Suppose Artbreeder used a model that was trained from scratch. Since it has a random initialization, its latent space wouldn't be compatible at all with nVidia's FFHQ model. Sliders on Artbreeder wouldn't work with nVidia's model, and vice-versa. A "blond hair" slider for Artbreeder would result in nonsense when applied to nVidia's model.

Artbreeder has an API, through which you can get the latent vector of any given image. You can use this to extract Artbreeder's sliders as follows: Extract the latent vector for a given Artbreeder image; move a slider to the maximum setting; extract the latent vector for the result; subtract the two latent vectors. Presto, you now have the slider.

If you add the resulting slider values to nVidia's FFHQ model, you will find that they control the same facial features on both Artbreeder and nVidia's FFHQ model. They don't match exactly – Artbreeder appears to be fine-tuned from nVidia's base model – but it's very close. So it's clearly derivative, and thus falls under nVidia's "no commercial usage for derivative work" restriction.