People in the rink said Ekholm was yelling at the ref and that's what made him aware of it.

I think it'd be an interesting wrinkle if one of the players on the ice when too many men is spotted served the penalty. Say the fourth line is changing for the third line with the shutdown D pair out. Well, now that team is almost definitely putting a PK man in the box, rather than someone unimportant to the PK.