I don't think he says that the whole picture is AI-generated, only the girl face. I don't know if there is already a software for that but AI-created faces are real. (Make-a-Face + FakeApp = Profit!)
You're right, hadn't thought of that, but I'd like to point out a few things. Make-a-Face does cartoony faces, not photo-realistic ones. AI-created faces would also still be a heavily restricted set of random values, no 'intelligence' involved. If you restrict the possible values enough, the resolution is at photo-realistic, and you run through enough iterations, you could come up with faces that pass as humans. That would still take a LOT of resources as just writing the engine and getting all those variables working would be a nightmare. (I mean just look at any of the more sophisticated character creators in games. Those aren't even photo-realistic, look at how many sliders they have, and note they are written by entire teams of people.) That high a resolution would also result in some serious memory usage and time.
I'm rather doubtful that this particular author has done anything like this. Its far, FAR more likely he has a pool of real-life faces to pull from, and just randomly selects one and says the 'AI' did it. He might very well use that FakeApp program to put the face on the body though, as that seems relatively simple.