Mechanical failures, despite proper maintenance, can result in the almost impossible "I didn't pull the trigger, but it went off!" scenario. This kind of thing is an accidental discharge (AD).
Almost everything else is a negligent discharge (ND). The user failed to do something he should have, or did something wrong.
The dictionary may help -
neg·li·gence Noun: 1.Failure to take proper care in doing something: "some of these accidents are due to negligence".
2.Failure to use reasonable care, resulting in damage or injury to another.
So, perhaps we are really arguing about "accident without negligence" versus "accident due to negligence".
What is confusing is that the media seems to use "accident" to describe anything that was done without intent. If so, I suppose our common use of ND is an accident. It's just one with negligence as the cause. And the media may not be aware of the virtual impossibility of a true AD, and they misuse the term if they try to describe what happened.
IMO, what is incorrect is to "brush over" the negligent aspects of an incident such as this and center on the lack of intent.
Of course there wasn't intent to cause harm. That just means the term "premeditation" shouldn't be used. It doesn't mean the individual isn't a negligent fool, or that he should escape punishment.