I didn’t see the game live, only on highlights. And this is the most plausible scenario I can come up with, based on what they showed.
1:The defenders hand is out in a “stop” gesture position.
2: The ball strikes the flat palm, not the arm and is clearly diverted away from where it was intended.
3: This is interpreted as a deliberate block or pushing the ball away and possibly the defender “trying to be clever” by tucking his arm in but using his hand and hoping to escape using the “natural position” clause.
Would I call that myself in a game? No. On the original camera shot in play, did it look a penalty? Again no.
But, given the stricter interpretation and implementation around Europe I’m not completely surprised at the call. It is far from the worst I’ve seen called in that part of the field.