Maybe hes learned the same tricks that I have heard about on the server, using macros. like how you can fast click to food and back to sword and still be moving and attacking, esp with hotkeys being the number keys above ASWD
The video is too fast to show anything but a failed attack and a good bit of lag. For example, my internet I am about a second to two seconds behind, hence why I don't partake in PvP, as it can get really unfair with being killed easily, or getting the drop on someone and laying enough kits that once lag sets in, you die almost instantly.
Seeing as the internet is the internet, there could of been lag enough to make it seem like he has his back to you, and that he typed while moving, but in reality he had typed that a while back, and had already turned to see you.
Edit: Also whats with the instant disconnect when you died bro?