I think both reds are correct.
Mitrovic is foolish, and completely wrong to not only push the official, but also to follow it up with aggressive behaviour (He was allowed to carry on like this all 90 mins v us in the first game of the season however. What excuse did they use then? Oh yes, it was the new allowable level of aggression or something, to keep the game flowing etc)
I do however think he has also been sent off because of the Fernandes incident against us (just like Mascherano was also sent off against them because of the respect bollox that was brought about because of the behaviour of the Man Utd players)
The big issue however is refs from Manchester continuously being allowed to officiate at their games. It needs to stop. It needs to be called out and highlighted. It's wrong.