As I know this opinion could receive a bit of backlash and be quite divisive again, I think it's only fair I list my reasons:
1. Ange greatly respects Pep from his time working in the City group and hails him as one of the best managers in the world, to the point that he has 100% adopted some of his tactics into his own.
2. Ange constantly talked in the build up to the game about "testing ourselves against the best in the world" in this Man City team. Ange is a born winner, and would love nothing better than beating who he perceives as the best in the world. In my opinion this is to the point that deep down Ange would've rather won this game over all our London derbies, as he views City as a bigger scalp than them.
3. This game of all games is where he finally decides to spring this new tactic from nowhere which was the first time all season in my opinion that we set up to counter the opposition rather than play our own game (By flooding the midfield with players and out-numbering City's box midfield).
My personal opinion is that Ange had this fixture targeted in his head all year as the perfect opportunity to test his wits against Pep and I think above all other fixtures Ange would have loved to have won this one going up against the best in the world.
This is partially in my opinion why the situation of this match drew so much furore from him in comparison to other bad results. He felt let down by the fans not driving on the team in what he perceived in his opinion to be his biggest match this season, but that opinion on the games importance obviously wasn't held by many of our own fans which led to friction.
T.L.D.R: Ange seen this as his biggest game this season going head to head with Pep. The lack of general fan support followed by the fan in the crowd calling him out for this preference led to touching a nerve, which resulted in Ange's outburst.
P.S. Still love Ange and am behind him 110%, now more than ever even and despite the fan potentially being right imo, that doesn't mean he has the right to repeatedly should it at Ange.