I had similar results, and story 4 is so trope heavy I wonder if it’s just an amalgamation of similar stories. The human stories all felt original, where none of the AI ones did.
I'm not sure I agree that the human stories felt original. I was pretty unimpressed with all of the stories except maybe 6, and even that one dealt in some common tropes. 5 had fewer tropes than 6 (and maybe as a result of that received the highest average scores from his readers) but I could tell from the style it was AI