Definitely photochopped. Let's think how shadows work. The shadow cast on a guy five or so feet in front of him is going to be larger than the actual object. It's the EXACT same size, with the EXACT same detail on the guy in front of him. This made me think that he created a black matte of himself (the guy in the white) moved it up a little, and thus cast a "shadow" on the shirt in front of him. The comment about the guys back not being a board is also correct, the shadow would warp. Secondly, the guy is casting shadow on both sides of himself (as if he made a matte and moved it). Most of us mortals here on earth cast shadow to only one side. And the direction of the light (pushing his shadow to the left) and the camera angle (behind and aiming slightly to the right) dont match.
But I must say, that is an excellent job.
Or maybe i'm full of it, and the flash has indeed done something strange.