I challenge everyone to find something warranting major penalty here:
For me it looks like Steele made a "butt-ending" motion (visible from video too) and referee saw that. Referee seems to have had a really good position to see the jab connect with the Korean player.
IIHF rule book screenshot:
So if the jab connects it is
ALWAYS at least a 5+20.
It is however kinda stupid to see a player get a major penalty, when nothing really seemed to have happened. Although it is the players responsibility to know the rules and play accordingly. Obviously the "butt-ending" was not dangerous, but this rule needs to be applied so the player learns from this and will not attempt to "butt-end" again. Because the second time just may cause something more serious.
Butt-ending, spearing, head-butting etc could be very dangerous so there is no tolerance in IIHF for these actions and the referee did not do anything wrong.
edit: after watching the video closely again, form behind the net cam (0:22) I can see from the way Korean players shirt moves/behaves it was quite clearly a "butt-ending" by Steele.