If he had only 12bb then he had a small, pushing M of 5 (M = stack / blinds + antes) and he was in Red Zone as described in Harrington's zone system.
He was in a prime shoving situation since everyone folded before him, his cards consists in vast majority of high cards and any ace. The fact he shoved from hijack means he had even more lower requirements since a lot of people were already out. Here's the kind of cards an M such low can shove:
22+, A7o+, A2s+, KTx+, QJx+
You may fear he have a bigger pair than you but a player gets a pair only about
5% of the time in general; If a red zone stack shoves, you expect 2 high cards or some Ax the majority of times where your
55 is 55% ahead.
Pairs are almost always deserve a call against such low M that can't hurt you. In fact, if you just call, you're probably giving good odds to the players next to you to call as well and break you post-flop. A better play is to isolate the low M by a re-raise; small pairs value is very much reduced when the board comes like A♥T⋄9♣ against another caller(s), especially with a bigger stack.
If i was early positions (eg. he shoved from UTG) i may have folded, mostly because of the number of players next to me waking up with a monster; against mostly the blinds i would isolate to be only against the small M that can't hurt me.
Long story short; having only the blinds yet to act and a 55% to win most of the time, by risking just 1/5 of your stack is just a great opportunity to accumulate chips by re-raising the small stack.