His arms were above his head, not sure you see many people wandering around like that.The position of his arms really aren't that unnatural considering the situation. It's not like he is trying to block the ball, his arms are in that position in order to maintain balance.
The natural position for your arms is by your side, there's been plenty of handball decisions given when people slide and their arm follows them and the ball hits it, while the player hasn't purposefully put his hand there it's an unnatural position for it to be in.