His hand, which was far from his body, stopped the ball, which was going towards an open goal/Krul. Stonewall penalty.
His hand was in a 'natural' position for getting him self off the ground, it wasn't placed there just incase a shot came it's way. Until humans evolve into a more streamlined mammal, you'll find that people cannot keep there hands 20cm from there cock at all times.
Tell that to the referees. When the hand is kept far enough from the body, especially when the ball is going towards the goal, it's a penalty.