Yes, the range might indicate removal of sights. But if he REALLY felt threatened, would he be that cool under fire?
Vang is ex-military. Depending on what his job & training in the military were, I'd think it is possible that he was that cool under fire.
Totally possible.
Do we know if he's ex-military? (We might, I just haven't seen it.) He certainly doesn't seem to be the ignorant non-english-speaking savage that some portrayed him as initially.
If he was really that cool, then he was "methodical" instead of "berserk". Either way I think the guy is toast.