even though we have photos of the holster in question,
even though those photos show the leather to be worn and having a crease,
even though that crease is shown contacting the trigger of the firearm that discharged,
even though though the report makes no mention of the user holstering his firearm at the time,
even though the photos make it obvious that the firearm would only barely be in the holster if a finger was trapped between the outer leather of the holster and the trigger to cause a discharge,
even though the location of the torn fabric supports the idea that the muzzle of the pistol was quite deeply inserted into the holster,
... you know what Really Happened(™)?
Sorry.... facts not in evidence to support your 'theory of the case.'
Going by the fact that it's legal to carry a concealed pistol in Texas (and illegal to openly carry one in most circumstances) there is no reason why the poster would had to unholster to eat and then have had to holster again upon entering his vehicle.
Further, judging by the time it takes to crease leather to that extent (and the wear is apparent in the photos), it had been going in and out of that holster for some time before events caught up with the poster and the discharge happened. It didn't 'just go off' and the poster never said it did. I'd suspect that it went off because the act of the poster twisting to his left to put on his seatbelt caused the pistol to shift in the holster which allowed the now fastened seatbelt to depress the trigger sufficiently and cause it to function when he again faced to the front.