Otherwise known as the flame war detector, which does a decent job of keeping flame wars off the front page but occasionally has to be fixed by a mod when it kicks in incorrectly.
Moderation is hard, and HN actually does a pretty good job all things considered.
It pains me to agree, but this is quite right: for every important developing story that gets erased like this, there's like 500 nonsense flamewars that guaranteed you don't want to read, that get erased by the same heuristic. It's genuinely tuned well.
(I'll never agree with HN's title-editing bot though. That thing's cray).
Moderation is hard, and HN actually does a pretty good job all things considered.
Edit: it's already back.