I'm not trying to defend the decision but if I had to guess why Sean got off easier I would bet that they took into account:
- Sean's 13+ years in the league without to my knowledge any other issues like this
- At the start of things, it looks like Sean could be trying to separate players from the two sides as he typically does in these situations
- Sean's actions came in response to Tanasijevic head-butting him so the harsher penalty goes to Tanasijevic for starting that portion of the incident.
If you watch the start of the situation Sean comes in from the side and pushes our guys and the TOR guys apart. He pushes Tanasijevic very aggressively and in response Tanasijevic head-butts him. I could be wrong, Sean could have been shouting along with the TOR players and coming in to fight but given how he enters the situation and his general positive reputation across the league I think it's plausible to believe the league gave him the benefit of the doubt and assumed he was trying to help and got head-butted.