Aguero looked at the player, knew exactly what he was doing, Mustafi didn't once look at Aguero. It was a nudge, a clever nudge. You could argue if Aguero doesn't nudge him then he gets the ball. Not complaining myself just don't think it was as obvious as a non foul as people have made out.
He doesn't nudge him, he just stands his ground, the impact comes from Mustafi's motion. The idiot didn't once check where Aguero was.