Reviewing the pictures released, I come to the immediate conclusion that this was an accident after servicing the weapon. Some of you familiar with the use of guns, you have to clean them from time to time, they get disassembled, delubricated, cleaned, lubricated again and then reassembled.
Now the last thing you do after everything is finished: You do a function control. For this reason you have to do a loading action and pull the trigger. Also to release the feather on the hammer, for some models, I don't know the H&K that well.
For some reasons the captain (it is obvious that the FFDO is the captain from locking at the picture) forgot the bullet in the gun, and he triggered. As a trained gunner you always point your gun towards the least dangerous direction when trying such maneuvres.
Now, wileydog3, of course I do know nothing about the FFDO program. That doesn't mean I don't know something that would help it to become more safe.
That is: No personal guns, it stays in the safe, unloaded, locked, sealed, and only will come into action in the real case.
Dani