For the record VALVe removed interpolation many many years ago.
His method of sniping is suspicious because it is a method many cheats adopt to avoid being spotted cheating. Aim at a corner of a wall (which would require insane reaction times to even hit the person) and wait for them come to you. You can tell that each AWP shot is timed (through aid of ESP or a wallhack) because there is ZERO surprise and reaction in his crosshair movement. They are all kills that are timed perfectly. When I snipe I don't sit as calm as a hindu cow and hit everyone exactly as they cross my crosshair, because I am not expecting them to come at that exact moment, in that exact place, jumping or walking or running. So of course there would be movement in my crosshair because I would need to readjust my aim in relation to their movement speed. He, however, just sits and leaves his crosshair at a spot where the enemy will cross, and just waits to time his awp shots.