This kill isn't super crazy or anything, you should know the general height of an upper torso/head while blindly looking. Also, as he runs up to the b tunnel entrance, notice that bullets are hitting the wall on the left. People are obviously shooting into tuns from back there. I automatically assume someone is behind either the front bricks, back bricks, or crate and going to shoot me.
You'd definitely need a longer demo, more than 1 kill, to prove hacking.