Doubt there is manipulation as you suggest. Your assumptions of HN demographics are being challenged instead.
Reddit, for example, also had these shifts, but much more so, since they don't even try to be niche in the first place.
I was surprised when I read the suggestion on the other thread. And it got me thinking, how would we know? How could we protect against it?
https://upvotetracker.com/post/hn/28149974 looks completely normal, the story is just interesting
What's a bot affected post look like?