Accidental discharge in a case like this is like describing a suicide as "killed while cleaning his weapon".
It doesn't describe what happened. In order for the weapon to fire, there had to be a round in the chamber. That's risky enough considering that even if the safety was on, it can easily become dislodged in an vehicle accident.
That's when bad things happen.
Like in this case.
Let's get a board of inquiry going right away and make sure the weapon doesn't have a problem and the battalion standard operating procedures are the right ones.