Now, the full video of the incident has been released and it still doesn't look too good on the coach who took matters into his own hands, video of the incident is from Pavel Barber, take a look:
It looks like the players got tangled up at the blueline and as one of them was going to lift his arm, he dragged the other on down, causing him to fall awkwardly and get knocked unconscious. I don't think there was any intent there for injury at all. It should've been a penalty for holding yes, but nothing more.
As an adult in the situation, you have to know better than to go after a kid. Accidents happen all the time, that doesn't mean you take matters into your own hands.