It's simple enough, plant rounds in their ammo caches that have had the powder replaced with C-4.
It could have very well been a planted round. "hot rounds" have been around for a long time, the us has used them since vietnam. great way to take out the enemy. At the very least you take a guy out of the fire fight, just think if that had happend in a line of fire. The guys to the left and right would at the very least not be having a good day.