That was not a 1 shot kill. If you care to notice, as he was being shot, the red blood injury warning flashed across his screen before he died. When you are 1 hit killed, as with a sniper rifle or in hardcore, you dont get the red screen effect, you simply die. Not to mention that the damage that was coded for each of the fully auto assault rifles does not allow for a 1 hit kill in non-hardcore.