Well, I think they are using a GA, based on: > Machine learning-based algorithms subsequently determined which faces produced the greatest amount of activity f

Well, I think they are using a GA, based on: > Machine learning-based algorithms subsequently determined which faces produced the greatest amount of activity for each person, then established which traits those faces had in common. Based on that data, the neural network then proceeded to produce new faces that combined those traits. In particular, it is a reasonably common idea (in the last few years) to use a GA or other metaheuristic to traverse an embedding space. Here, that embedding space is the z layer of the GAN. Especially when "fitness" in the embedding space is purely subjective, it's natural to use an interactive GA. However, I am over-stating it to say that the field is just interactive GA. It's that, intersected with face-GANs.