If you watch it closely its actually Young who throws his arms out at the defender 1st. But he is a top class cheat and even cheated against his old team Villa which sums him up perfectly.
The biggest concern in this though is he keeps getting penalties and free kicks from refs. Its like the fairy tale "the little boy who cried wolf". if I was a ref and he went down, even if it was a penalty I would not give it as I would assume he dived. Managers in their press conferences before playing Utd should mention his diving (and others in Utds team) and say they hope the referee is strong enough not to fall for it.
It is clearly practiced at Utd as so many of them do it, all go down in unnatural body positions and all of them, even if no contact shout in agony to ensure the ref hears it.