i think any time a weapon is fired unintentionally it is due to negligence. theres no other way i would label a discharge.
IMO dropping a gun is an ND. Even if it falls off the shelf or out of a holster. Who put it there?
Mine was years ago with a German Mauser. Had one chambered and put the safety on to adjust the sling. When I flipped the safety off, it went bang. Note that my finger was nowhere close to the trigger, since I had my hand on top of the stock to move the safety toggle.
I tried to recreate the incident, but never could. I never used the safety again - I just partially opened the action instead.
I really don't believe in freakish accidents. There's always something someone could do to prevent a negligent discharge.