Sure, it may be not that simple. But: Take a look at the video between Minute 1:06 - 1:50. Look at the upper right corner. His FPS NEVER go over 60. This is a 100% indication that he has VSYNC ON!
He MAY has turned it off for his later tests. It is hard to tell, as he is never filming the upper border of the screen during those tests. But the fact that VSYNC is ON during his game play makes it more likely it was on during the test itself.
But for good measure. I will make my own Video with a similar setup.
Also I am not defending Argo/Arma here. The engine has performance issues! But in Argo with 10players max and no vehicles it is not really an issue in my experience.
But in the case of his video something must be wrong with his setup. May it be graphic settings, VSync, or his computer. I don't know. But what I know is that there is not such big input lag "in general".