It's weird that this crap never occurred until Barry and his Nazis started pimping the the destruction of the Bill of Rights. This crap was intentional.
It went off when he was removing it from the holster so the safety personnel could affix the security strip. The round struck the concrete floor and ricocheted up into the calf of the guy manning the ticket booth at the entrance.
I was about one hundred feet away, looking at a really nice 1911A1 when the round went off and just about everyone in the entire building (probably 20,000+) hit the floor.