Or, he negligently discharged his sidearm because he felt a need to put his booger hook on the bang switch and made up a story. :?
I would be shocked if it was truly an accidental discharge, due to mechanical issues with the glock. Glock sells a ton of pistols. If their guns "just went off" in "freak accidents" when carried in bags, even rarely, then there would be a constant string of lawsuits.
Also, I personally don't like off-body carry plus condition one (round in the chamber). I just feel like it is too hard to keep the pistol pointed in a safe direction 100% of the time with off-body carry, or if in a large compartment (like this cop was carrying) there's just too much risk of junk rattling around in the bag and somehow getting in the trigger guard.