Oh so you have a crystal ball do you? Lee Mason would have sent Xhaka off. It's nothing to do with the size of the club - it's the standard of the referee. As Oliver is a very good referee, he used his common sense and didn't treat the rule book like the bible.
On this one Tom, I definitely make you right. Fair play to the ref for using common sense. A sending off in those circumstances would have ruined the game unnecessarily.