I think McCallum had a break through season and was able to control his antics all season on the most part. I feel DM really likes him and you could see that moving him up on the first line, PK, PP. etc
I think the penalty McCallum took was undeniable bad brain fart and set off DM fuming in between periods, in the heat of the moment. Once coach loses his sh@t at the moment told him to pack up. I really believe he would have done that to any player that would have taken a timely bad penalty like that. I think it's more of the nature of the penalty, by tripping the goalie during the PK. If he took any other kind of penalty during the PK, like a trip on the forecheck, I believe DM wouldn't have lost it.
I believe DM is in McCallum corner, anyone that has coached before knows these things can happen, it can get heated especially during playoffs.