Smaug, look at the video again.
The holster he was using EARLIER used a thumb-release near the safety. Which, admittedly, is dumb - ESP. with a 1911 pattern.
But that's not the holster he was wearing when he shot himself.
What happened when he shot himself was, he hit the "holster's thumb release switch" that wasn't there because he'd switched holsters, and instead switched off the 1911's safety very early in the draw sequence. This combined with the Serpa's main flaw to produce an ND.
The Serpa's main flaw is the location of the release switch. You're pushing inward on this button with your finger. As you continue the draw, if you keep pressing right at the same point, whoops, you hit the trigger.
And that's only the first of three major flaws in the Serpa or anything else with a release button near the damn trigger!
2) If a piece of grit gets under the release button, your gun is frozen in the holster.
3) If you walk up behind somebody dumb enough to wear a Serpa in public, you can rip the entire gun and holster "core" right off the belt mount by rotating the grip down and then out. In less than a second. If the poor fool is REALLY lucky, there will be a piece of grit under the release mechanism and you'll have a club in your hands instead of a gun.
DO NOT buy a Serpa. If you have one, toss it in a campfire or wood chipper or do your own Blend-Tech[tm] parody commercial (and I assure you, yeah, it'll blend - probably with a fairly cheap blender).