But when José Sa flew out and slapped a Leeds player in the head it wasn't a penalty even though he didn't touch the ball because reasons, and to everyone's surprise nobody went apoplectic over it.
Found the Martinez incident. Full game available here, timestamp 1:13:45
https://www.manutd.com/en/videos/detail/full-90-video-of-aston-villa-v-man-utd-on-6-november
Regardless of getting the ball or not, you can make a case for recklessness, carelessness or endangering the safety of an opponent. Running full steam at an opponent head on and hitting him in the head with your hand is much more dangerous than running backwards and turning into a player that's not running towards you at full speed himself and making body-to-body contact.
For what it's worth, I think it should've been a pen and I'd have been livid if we'd been denied one in the 97th minute a goal down. What irks me is the utterly disproportional reaction to a "normal" foul when much worse fouls have barely caused anyone to raise their eyebrows and just comment that "well goalkeepers seem to have bigger freedom to do things in their box".