The video leaked online. He is not even trying to reach for his pajamas or something. A cop asks him to move towards them and the next second you hear the shot. It's crazy.
He definitely reached for his shorts. It's a reflex that comes from a whole lifetime of being able to pull up your pants without risk of being shot.
But that's all irrelevant. If the cops were only interested in securing him, they would've made him lie down like a starfish and have someone approach him instead of letting Jigsaw make him play Twister.