In truth it's not an easy law to define. What distance is close? ....Had the ball not hit the lads arm/hand it would have hit his chest. He didn't change the direction of the ball....which was a factor....it was a 50/50 call sometimes you get them, sometimes you don't.
It comes down to common sense, ot at least it should.
We all know when the distance is considered too close, when it’s basically impossible for the defender to move his arm out of the way due to the short distance he is from the ball and how quickly the ball is moving.
On this occasion, the ball came from the corner flag. It’s completely irrelevant whether there was intent, the position of the defenders arm or whether the ball changed direction or not.
The fact is, the ball hit the defenders arm after travelling some way without any real power. The defender lost concentration. It was a penalty.