Seems to be using some combination of wallhack and humanised bot. In other games, his rails always hit the legs (as if his bot is configured to shoot at cg_enemylowercolor).

He has changed his name to "5kull_" since this demo was recorded (obviously to avoid the cheating accusations I had already levelled on him)

I think it's pretty obvious from this video, let me know what you think.

Please note that this isn't about having perfect aim - it's a humanised bot. His aim seems to consist of 5-6 'micro' movements in the last quarter of a second of 8:44, and again towards the end of 8:46

Edit: Also please watch this demo before you comment, follow his POV. - or watch on youtube

Short clip showing targeting through walls/floor