The BlueSky post has another interesting clue. The pencil sketch on the right. Seems possible a human artist drew the sketch, then had an AI model "colorize" it. And in so doing, maybe the AI model added the 3 genAI tells/artifacts I identified above.

the scarf matches the one Rich is wearing near the end of the documentary. the code matches what's on the Clojure source code, even if it's an odd choice. the two belts are in the draft, even if only one of them features the logo. the artist's instagram has a bunch of well colorized artwork. I believe it is really human made

That wouldn't be very interesting at all. It's just a thumbnail on a niche programming documentary

There’s nothing odd about two belts in this situation. One is the belt for the pants and the other is the utility belt holding the pouches. You need to be able to add and remove the utilities without having your pants fall.

The weird choice is having a belt and suspenders. That only works as a fashion choice, which makes little sense for an explorer.