I also think Arsenal deserved the win, if not for anything at least for the fact that they were able get the first goal on the home ground of the opponent, nevertheless the mistake that led to the goal wasn't the fault of the goalkeeper but negligence on the side of the Manchester United players (defenders) who couldn't protect their goalkeeper from being distracted by the arsenal players.
Arsenal played like they were sure of winning the match, which they did, while the Man U team displayed much effort from rigorous training enough to win the gunners. But, they weren't just lucky, and David Raya wasn't fed with powerful shots, his seven saves, and the kicks from Man U forwards carried lesser weight, except for the ones that went outside the goal post.