One element could be the timing - if 5 points appear in the first, say, 15 minutes, it might be enough to raise it to the front page? Maybe there's an element of randomness, too. Dunno.

I suppose HN algorithms are secret for a reason - if they were revealed, they could be optimized for.

What's the second-chance pool: https://news.ycombinator.com/item?id=26998308

But then it needs more votes in a short window to stay. If it doesn't get them, it drops off as quickly as it came.

So this seems to be HN working as usual.