My first thought would also be that it was a fake as people could not be that stupid. But I have seen troops do some really stupid things at times and I am one of them.
Why hold the plate up instead of putting it on the ground?
Why have an Afghan fire the shots?
Why make such an elaborate fake?
For arguments sake lets assume that the strike is real, and if you were to use a squab why not put it closer. They do not seem to have seen the strike as they would have realised that they were well off, one would hope.
If we assume that the strike is real and the firer was a competent shot, could aim the rifle, as they advanced the probable impact of the next round would be diagonally moved to the right and up towards the point of aim. The guy holding the plate seems to have been hit by the second shot in the right leg which would be about he place I would expect to see the next strike.
I would add that I too would have expected the guy with the plate to fall like a bag of shit if he had been hit in the leg, but he just seems to keel over.