Sorry, I mean it was nearing the top of the homepage, and then it was removed from the homepage. The post still exists (hence my link to it in the original post).
I believe new posts are weighted a bit higher - but there is also some threshold going from "new" to front page. This appear to me to be a typical "almost interesting" (as judged by up-votes) - made it to the front page, but then got overtaken by other posts.
Ed: the current code behind hn isn't open source, but it might still resemble this to some extent: https://github.com/arclanguage/anarki/blob/master/apps/news/...
I'd have guessed that it was a part of some sort of filter - perhaps a "voting ring" was detected or something, but I'd really like to hear from a moderator, or something, because this seems a bit strange.