What makes you think the cover is AI made? Assuming you talk about the new 1.0 release image. Does not look particularyly AI made to me.
This game has like 5k reviews on Steam, over 1k in the last 30 days. I would suspect they could hire someone being able to draw a piece of art work for release and promotion. There do be real life artists that can draw like that. There still needs to be something for AI to imitate...