Fact is that Mousset was offside when all is said and done. No bad luck in that. The Man City players were appealing instantly and straight after the 'goal'. The linesman has been told to keep his flag down in close situations, if they really have to do that then they really should add an instruction for him to put his flag up and call for a check when the ball enters the net.
The VAR official could not overturn their first goal because there was no rule broken. The onfield referee should have stopped the game ( whistled) before Aguero shot. After he scored there was no way back, no rule to stop the goal.
Great shame a poor ex-referee like Reilly has been running this project. However referees do not make the rules of the game, as far as I know.
We were not 'diddled' yesterday, but very unlucky.