It seems unlikely that this is algorithmic, hence, I would guess if a post is deemed to not be meeting HN standards / guidelines, moderators can "demote" a post, essentially removing it from the front page. So in this case, was the title simply too link-baity? And who judges that?
This is obviously a guess, and looking through the FAQ (Official and unofficial!), I can't seem to see it stated anywhere.
Another possibility could be user flagging, but that would seem too easy to game maliciously.
I think whilst some elements of your filtering you want to keep secret to stop spammers, it would be helpful to understand this throttling behaviour to help people submit better content. Transparency is often helpful to create less work for both sides, so if an answer could be given, I think people would be interested to know!
i don't know how current it is, but i believe that hn source is included in the arc download - see http://news.ycombinator.com/item?id=1390685 - so you could try looking there to see how flagging is handled.
This is obviously a guess, and looking through the FAQ (Official and unofficial!), I can't seem to see it stated anywhere.
Another possibility could be user flagging, but that would seem too easy to game maliciously.
I think whilst some elements of your filtering you want to keep secret to stop spammers, it would be helpful to understand this throttling behaviour to help people submit better content. Transparency is often helpful to create less work for both sides, so if an answer could be given, I think people would be interested to know!