I was surprised VAR didn't get the referee to look at Martinez clattering Elanga. He palmed the ball away with one arm, and smacked him around the head with the other. On the ground, if you nick the ball with your right foot, and follow through with the left, it's a foul, regardless of if you 'got the ball'. Or it certainly should be if the referee sees it (funnily enough Casemiro did that exact thing in the first half, which wasn't given and probably should've been)
If Martinez catches Elanga with the arm he palmed the ball away with, then I don't think it's a foul, but catching Elanga looked like a separate motion and with a different part of the body to the one that won the ball. If it was given against us, I'd be lambasting De Gea's recklessness, and not the decision.