I tend to agree that this sort of excellent performance is not a matter of going over scenarios in one's head.
It appears that the guard was well training and practiced in the fundamentals: drawing his gun smoothly without wasted motion; delivering accurate fire quickly; moving; and using cover. He apparently was able to perform those mechanical tasks well and without conscious thought and was thus able to focus his attention on the situation as it unfolded and make good choices about how he responded.
"It is long been a principle of ours that one is no more armed because he has possession of a firearm than he is a musician because he owns a piano. There is no point in having a gun if you are not capable of using it skillfully." -- Jeff Cooper