My thought... they were both on the roof. One got pissed, they started fighting, the guy with the nails in the head obviously got the woirse end of the fight.
Being a superintendant fo five years, and on the job (construction for like 10 I've seen it all. I've seen crowbars stuck inside a guys leg (co-worker was pissed). I've seen people hit in the head with a hammer (again, dont piss your partner off).
On my steel crews I had three guys putting in 1x4 and insulation. This guy nailed his carpenters leather belt to his hip bone.
Two weeks later, he was on the same job, and nailed his shoe to his foot (through the heel). If anyone would have nailed himself 6 times, this guy was it.
Due to the nature of the nail gun, I could see a rebound type effect and siz nails in one spot, or near each other, but six nails in 6 different spots..they wre fighting.