He tried to defib some one and he happened to have a psg attached on him this could be because of a bind. that he accidently pressed.
After holstering his defib it would switch automatically to the the big gun if he had one equiped.
its not like he started showing it around the world and yelled down his mic that he had a big gun in his hand the moment he noticed that he had a big gun in his hand he nocliped in the ground. which was the right thing to do.