I haven't played for a week (due to various health problems, nothing serious though), so I've checked the players only occasionally.
This dude, when the map started, looked like he's getting his score by going against complete pushovers (as seen in the beginning and the end of the demo); however, within twenty or thirty seconds I noticed his crosshair movements are little suspicious. And indeed, in the end I didn't even need to replay the demo to be 100% sure he's using wallhack.