Yes, i get that. However;
I reiterate not having a strong feeling on this, but playing devil's advocate; I'd say he lost control of the ball because the dominant motion was him falling onto Wellbeck when he should have punched. 'All players have a right to their position on the field of play' and so on...
'should have punched' isn't even close to being relevant.
And the ONLY reason he fell onto Wellback is because Wellback ran into him while he was in midair. The ONLY reason the keeper lost the ball on Wellback's head was because Wellback took him out in midair.