Perhaps one of the guys with orange arm bands didn't see it. Can linesman suggest referees cite infractions they didn't witness?
“Officially” (heh) speaking, a linesman can report to the referee an infraction he witnesses that he (or she) believes warrants a major, misconduct, game misconduct, or match penalty, at the next stoppage in play that naturally occurs, but may not stop play on their own to do so. I believe that they can also do so for something that warrants a double minor in the NHL (such as a high stick that draws blood - speaking of which, the case of a high stick that draws blood in USA Hockey rules is defined as “injuring” an opponent with an infraction, which is automatically a major plus game misconduct, so it works there - but it’s rare to happen since most amateur players wear full facemasks). The referee will then decide whether or not to assess it, although in practice (and in my personal experience) it’s rare for a referee to not listen to the linesman on this. A linesman can also stop play for the puck going out of play, the net coming off its moorings, or an injured player.
Unofficially and anecdotally, one time I mentioned in passing (I wasn’t really trying to frame it as saying that it warranted a major) that some kid punched another kid in the mask with his glove still on, and the referee gave him only a minor for roughing. He was not technically supposed to do that - although the kid clearly deserved a penalty, you’re not technically supposed to only assess a minor penalty for something reported by the linesman. At least, not at the time - I think USA Hockey expanded a bit what linesmen can report, but that was after I had stopped officiating.
Edit: forgot to add, linesmen are vested with the responsibility of calling penalties for too many men (referees can as well but the linesman, especially the one on the opposite side of the benches, has the best vantage point for noticing it), and since they're the ones who conduct almost all faceoffs, they call faceoff violations, two consecutive ones which result in a minor penalty for delay of game. They can also blow the play dead for premature substitution of the goaltender, although that's a very rare occurrence - I only had to call it once in my four years as an official, and we were working the two-man system that game anyway. That one's not a penalty, but results in a faceoff at center ice.