There is something called sound, use it and you will hear em coming, thats why he knew where they were coming from.
Seriously... l2P
edit: campers loose concentration at the moment there is too much noise to know where you're targets are coming from. Flashbangs, grenades, smoke, verything makes em shoot like 5 year olds. Remember, all his shots were almost perfectly shot. So he knows where to aim at various distances for headshots. These fuckers are very annoying.
Or just do what I do in these kind of games(havent played black ops yet). Watch your teammates and be sure to follow em on a certain distance. When they get shot you have all the info you need. Meaning you know exactly where your enemy is
Yes I know, im evil.