There is no evidence of this, no reproduction of it firing without the trigger being pulled, and not even a good theory on it. The YouTube videos are involve pulling the trigger far enough to disengage the internal safeties.
If the gun was able to fire by itself, without the trigger being actuated, then someone should make it happen on video. Shake the crap out of it, bang on it. Take it in and out of a clear plastic holster 1000 times until the supposed defect happens.
Here, the police officer isn't even touching his holster.
Regardless, if there is a defect in that particular gun, they should just demonstrate it. If it isn't the holster, or something in the holster pulling the trigger, make it happen outside the holster.