Sir, with the up-most respect I will call the cook off more negligent than what is shown in the video. A firearm left unattended with a loaded chamber is something I always address in my Safety Classes.
I was a Firefighter for 21 years and a great majority of rural house fires had loaded firearms in them. We would asses where the barrel is thought to be pointing and keep that area clear of personnel.
After more than 30 years as an EMT I have seen a few accidental's and many negligent and many criminal discharges. I also believe Mr. Tex has every right to call his accident a negligent discharge if he so chooses. I would myself had this happened to me.
Have you reviewed the video with scrutiny? The manipulation of the safety when he was mistakenly trying to release the thumb drive release is not visible but the manipulation of the Surpa release is done with the trigger finger pointing downward with no curl towards the trigger and again because of the out of time release of the pistol, (Tex pulling his trousers up) the reflex was to increase his grip of the pistol.
Now I have never seen this man draw previously and maybe he has a tendency to finger the trigger before he should and if that's the case I will also say this is a Negligent Discharge. After all this is a Human, not a Machine.