Ask HN: How come this submission doesn't appear in the frontpage?

Apologies in advance if this is an RTFM-style question.

I came across this HN submission: https://news.ycombinator.com/item?id=36326926 on the frontpage of HN.

However, I just searched from the frontpage down to submission #150 and it appears nowhere.

As of now, it has 46 points and is 53 minutes old.

How is that possible? Am I missing something? Aren't non-flagged posts ranked solely by their upvotes/age ratio?