Question about suspiciously good sniper

So I noticed that one sniper on the server was getting a ludicrous amount of kills. My first thought was "damn he's good", my second was "why aren't any of the spies on our team taking him out?". So I switch to spy, go invisible and creep up on him...and he headshots me. Multiple times. While fully invisible.

Is there something I am missing about this guys ability to notice spies, or was he just straight up cheating? Sniper is my least played class so I'm not really an expert on it.

Note that I wasn't on fire, or taking damage or bumping into anyone. I also used the CnD so that my invisibility didn't run out. And he got me multiple times while 100% invisible.

Possibly aim-botting too seeing as he nailed me the instant I wasn't behind cover. But he might have just been really good, so I can't be sure on that one. But I guess if he was a cheater, why stop at just one cheat?

And how well does VAC deal with this? If he just created a new account and loaded up TF2 FTP would just the account get banned, or would it ban the machine or the IP as well? If it's just the account then the FTP nature of TF2 could leave it wide open to griefing.

EDIT: Glad to hear that everyone has confirmed my suspicions. I was pretty sure he was cheating, but I've seen lots of stories of people getting reported by noobs who don't understand the game so I thought I should just make sure.