There is a very good reason for this as well.
Speculation has begun to percolate that Montgomery could lose his job if the Bruins continue to struggle. After all, this year has been the team's worst start by far since Montgomery took over. With that being said, it appears as though the team is responding well to his moves. Not only did they get the win tonight, but even Pastrnak himself didn't take it personally which is a good sign of a good relationship between him and his coach.
Charlie McAvoy revealed after the game that Pastrnak was still being a leader in the 3rd period despite the fact that he wasn't playing, which is not only a sign of a good leader, but also a sign of a healthy team culture.