Man this one is tough, because he looks the gun into the holster. I see he is wearing a separate undershirt, maybe that’s what got caught? The other thing is, he goes to top the mag off with the gun in holster. I wonder if when he shifted the gun removing and reinserting the mag, that’s when the shirt got caught?
I’m really inclined to say this was a wardrobe malfunction, because 1) Modded gun seems more likely to go off when he chambers a round. 2) he was finger banging the gun 30-seconds prior. 3) 99% of IWB and AIWB NDs are clothing related with reholstering having happened in the previous 60 secobds or so.