Goal scoring opportunity has nothing to do with it
You can quite literally be just inside the 18 yard box with your back towards goal and have someone go through the back of you and you'll be awarded a penalty.
Pogba conceded a penalty when he handled in the area and that wasn't goal scoring opportunity as it would have clattered into his face. The penalty correctly stood though.
Anyway this is the last I'll be engaging with you on the subject as it's clearly pointless with that gem. We've been awarded plenty of non penalties this season, such as the one against Villa and also the one against Copenhagen.