Normally, extended reach claims aren't too legit. This is because of lag, like, one persons screen is different to someone elses so they can hit you and you can't hit them. In this video we can see it is extended reach, It can't be the normal laggy delay. In this situation. British is in a stationary position where he can't hit past the wall yet pyro hits him from the other side of the wall. either pyro managed to glitch into the wall and hit from his client with major lag or he has extended reach.
We only have a small amout of evidence but we hope it's sufficient as he did it to even more of us before this instance too.