I think you guys are missing the point entirely. The holster had NOTHING to do with the ND. The fact that he curled his finger on the trigger and squeezed it as he drew was the reason the gun went off. He admitted this himself in the video. You could keep your gun holstered in a wet napkin and the gun still wouldn't go off unless you pulled the trigger.
I wear my G23 in a serpa and when I practice drawing it, I hit the release and keep my trigger finger straight when the gun comes out. The finger rests outside the trigger guard automatically and then goes on trigger only when I am ready to fire.
No offense to your friend but this was a negligent discharge all the way, he needs to remind himself of the 4 basic firearms rules while he is recovering. I am very glad he did not hurt himself more than he did. Hope he has a speedy recovery.
Be safe out there guys and gals!
Brain (Use this one the most)