He's definitely not hacking. There was nothing special about his aim, he used 1 Heavy Shotgun which explains his hard PBs and I believe if you rewatch the last round of your replay - it's a proof he didn't use ESP: He was waiting near the door for someone to appear from the stairs and then decided to go back, literally half a second later someone came from the direction he was previously watching and shot him from behind.
Declined.
