You probably have no idea what you're talking about.
Hold on. Let's check.
Hands up, any commandos on the forum?
Not I, but everything I was told in the military and have seen in semi-realistic military fiction is that you always shoot for the chest/center of mass so that you have a much better chance of hitting stuff.
Aiming center mass is good when shooting at a distance but if your opponent is only a few feet away... I was no commando but we often did firing drills where we would aim for the head while moving. It's not much of a stretch to me for someone with much more extensive combat training to get a head shot in a split second at that range.