@ Hidi,
Seems like there is a pretty good chance he is cheating. I found another log where he did 600 DPM and 99 headshots. I find the number of headshots the most unbelievable. 600-700 DPM sniping in HL is do-able (I've done it a few times), but never gotten near 100 headshots, nor have I seen anyone else that I know is legit get anywhere near that many in a single game... http://logs.tf/783821?highlight=76561198121171963
Have you looked to see if you can find any STV's? Try to find his sizziling stats profile and see if there are any STV's. Or if you played a recent match with him that was hosted on serveme.tf, go there and try to download an STV. If you can find one, please link it here. I can look as well, but I thought I'd ask you first to see if you can come up with an STV.