Perhaps what this is pointing out is that a lot of writers of the genre of "fantasy" produce mostly formulaic, trope-laden piles of crap that AI is pretty good at mimicking?
It does suggest that publishers might want to screen new writing with a quick "Did AI write this?" and only publish the ones where it is obvious to humans that AI did not write it.
Yes, the human-written stories that I guessed wrong about were the ones that seemed to have nothing to say. When the plot's stereotypical and trite, there's no subtext (difficult to do in flash, but not impossible; some can do it well), and it scans like anyone could have written it anywhere or anytime, well, that looks like AI.
(In that vein I am baffled how anyone could think the fourth story, especially, was anything but AI.)
(And, as well, the seventh story is interesting because it reads, to me, exactly like someone who's used to writing something longer trying to write flash. It doesn't land anything, it doesn't conclude, but it looks like if it had about twice the length it might be interesting. And it's got some dissonance from breaking with the usual demon-bargaining template. So I pegged that as human. Oops!)
I thought it was interesting/telling (but maybe not surprising) that the AI-generated stories scored the highest according to reader rankings, yet pinged to me as immediately flat and generic. But I really liked the idiosyncrasies of a few of the human-authored entries!
This is neither new nor news. "The Well-Tempered Plot Device" is almost 4 decades old (see: https://news.ansible.uk/plotdev.html).
It does suggest that publishers might want to screen new writing with a quick "Did AI write this?" and only publish the ones where it is obvious to humans that AI did not write it.