You're not the first to ask the question.
He's mainly a vCTF player. Has the aim but not the refined movement skills you've developed in DM gametypes.
If you have suspicions of people demo them. Watch it back. Note times and what you see that's "not right". If you can convert to a video format at high res then even better (my install seems to GPF whenever I play a demo) so I have to ask the other admins to look if it's a demo.