Evidently he wasn't as immune as you say and he collapsed and had to be taken to hospital. A shot to the head or the heart or some other area that would be immediately fatal and would have killed him. He was apparently not shot in the head or the heart or spine. Your opinion isn't based on any knowledge or facts. There are historical accounts of people continuing moving after being shot multiple times. As far as is known, the defector was shot multiple times, survived and was taken to hospital where he was operated on for these injuries.