How are submissions algorithmically generated on HN?

I've noticed by observing HN submission feeds that some clear clustering of submissions occurs as topics with a common theme appear in the same time window or cascade from earlier posts. It's even possible to trace that over days.

Now, this seems entirely natural for a community "exploring themes together" and vibing and riffing off interesting ideas.

But occasionally the serendipity seems bit too much, as if some broad level topics seem a bit forced. That leads me to the suspicion that the submissions process is not as organic as some may believe.

It would be nice to have more transparency around that.