Foxthe headshot attempt on the medic appearing from behind the crates at 4 minutes 15 seconds looks like either he has one of the fastest reaction times ever,
it's also slightly less suspicious that his mouse didn't move at all for the shot. kind of n obscure thing to say, but throughout the video his mouse "flicks" when he clicks (like most people with medium/high sensitivity, even sometimes low), just a bit odd when combined with the insane reflexes of that shot.
edit: going to summarize my opinion from steam chats with bloodsire. if he is hacking, i'm betting that he's actually a pretty decent sniper even without. with that said, you can't claim anything based on this video I think. 1. it's a frag video 2. [trying not to sound conceited] while some of the shots were suspicious, I feel like even more were shots that I used to make back when I was good at sniper. 3. it's a frag video.