Did you ask jamppi?
(valve agreed in court that jamppi wasn't the one who cheated)
But seriously, can vac be triggered without cheating?
"VAC is a component of Steamworks and the Steam client, and works by scanning the users system for cheats while your game is running. It works a lot like a virus scanner, and has a database of known cheats to detect. Once a cheat has been detected, the user's account is marked for a delayed ban."