If the rule is, if it hits the hand at all, regardless of the situation and the position of the arm, then yes it is a penalty.
It would be good if they can explain why other more obvious ball hitting hands, have not been given and it will be interesting to see future decisions.
I am not sure on the exact wording of the law, but I thought position of the arm comes into play, i.e. unnatural position, his arm is more or less in front of his body.
I suppose that is the issue, they should make a rule for it, because there doesn't seem to be one and they are making it up as they go along.
They’d argue that his hands not in a natural position, it should be tucked into his body rather than flying at head height.