We aren't talking about stats we're talking about finishing. They are not the same thing.
Total number of goals scored means little if it takes Sterling 20 shots to get the ball in the net once vs someone who only needs four or five shots. Man City create much more than us which is obviously going to help Sterling get his total goal numbers up.
Sterling is actually a bad finisher and one of the worst in the PL when it comes to one on ones or hitting it first time.