Let's be realistic, you don't ask a cheater or a scripter whether he cheats or not, only stupid ones would admit and even if they do , it should be taken with a grain of salt.
Groundstrafing is known for getting you to absurd amount of speeds, especially combined with developer 1 and high fps (that is on the old version of the game, which I assume you're using. Different commands on the new version though). It's even easier while combined with a hyperscrolling mouse.
That being said, it's not really cheating or scripting but it does give you an unfair advantage although I'm not quite sure about Ambrosia's regulations as using the commands I mentionned earlier so it's up to you guys. One thing that is sure is that he's not scripting or cheating and he should in my opinion be unbanned.