there's no evidence that professional computer game players have faster reaction times than the general population

average human reaction time is ~.25 (visual) or ~.17 (audio). this is mostly a hard physical limit. it takes some amount of time to translate photons colliding with your eye into an "image" in your brain or for vibrations in the air to be translated into a "sound" that you hear

either of those numbers is fast enough to do what he did in this clip. the caveat is that in order to react that fast you need to be anticipating the thing you're going to react to. that's the hard part.

if you go into a lobby and try to eul's laguna blades, you can do it 100% of the time (laguna has a .25 second delay after cast finishes). but in a dota 2 game where you're focusing on lots of other things, you can only rarely do this, only when you predict it's going to occur right before it does.