Should players come onto the ice from their players’ benches after the period ends and prior to the start of an altercation, they shall not be penalized if they remain in the vicinity of their players’ bench and SECTION 6 – PHYSICAL FOULS NATIONAL HOCKEY LEAGUE OFFICIAL RULES 2021-2022 78 provided they do not get involved in any altercations.
And
70.10 Fines and Suspensions – The first player to leave the players’ or penalty bench illegally during an altercation or for the purpose of starting an altercation from either or both teams shall be suspended automatically without pay for the next ten (10) regular League and/or Play-off games of his team.
There is nothing wrong with Pietrangelo leaving the penalty box (assuming he was let out- there is an issue that the timekeeper should have held him in until the skirmish was over). The issue is that he needed to head straight to the bench. Instead he went straight in and engaged a Panthers player before anyone engaged with him. It's not Vegas hate, it's literally just asking the rules to be applied. The NHL rules determine the penalty box and bench to be one and the same at the end of a period. I believe the Hockey Canada rules are even more clear with it being an automatic penalty to leave the box if there is a fight on the ice whether you get involved or not.