Looks like he fiddled with his gun after that. Wonder if he accidentally released his mag and had to retrieve it.
That is exactly what happened. You can see he bends down to pick up the mag; reinserts it into the bottom of the pistol (which at this time would not have a round in the chamber) and then retreats to his car. He even fiddles with the pistol as he retreats. He was either trying to rack the slide or the mag was empty or both and the slide locked open on the empty mag.