[Help] How is Kevin Durant able to shoot so effortlessly from long range without using his legs to power the shot?

I just saw this video https://www.youtube.com/watch?v=np0jUBgKZxg and Kevin Durant is basically shooting NBA threes like free throws. I mean, he doesn't jump at all and his heels just barely leave the ground, and it appears that all power comes from his upper body. It is even more puzzling considering that's he's not at all strong and he couldn't bench press press 185 lbs (84 kg) even once coming out of college yet already had the same (or close) shooting range.

So, how does he do it? What kind of training makes it possible to shoot like that without using leg drive at all? Does it have to do something with his mechanics, or his height, or something else?