Slamming his stick multiple times, slamming the bench door shut, and screaming at the referees for more than a few minutes was enough for him to be assessed an unsportsmanlike conduct penalty. Marchand is a player who can usually walk the line flawlessly without taking a penalty to harm his own team, but today he must have said something that crossed that line.
Honestly in this specific case, Marchand is completely right to be yelling about the missed call. Johnson's hit was direct knee on knee contact, the kind of hit that can end careers, especially now that Marchand is getting older now at 35. It's a deserved unsportsmanlike penalty for the tantrum, but Johnson should've absolutely been penalized for this hit, and the tantrum wouldn't have even happened.