Ok..so after viewing this demo quite a few times. I came to the conclusion that he is walling.
I wish the demo didn't lag either, cause like others said, he does have a weird shot with the AK, which I have seen in other demos.
But anyways, these are the ticks I got (these might not be exact ticks, I didn't feel like watching all over just to get the exact ticks)

2400 - looks up top (yes, this can be explained if you played this map before)
4600 - looks up at bridge and waits until his head pops out (couldn't hear this guy at all)
8700 - traced guy through corner wall (guess it could be typical that he was waiting there)
10800 - Shot upwards somehow with guy at stairs (not really a big deal, just thought I'd put it out there)
14500 - "Didn't see him" If his walls are same as when watching demos with matwire, then that explains why he "didn't see him" (not a big deal)
20200 - This one makes it obvious. He aims at the corner tracing guy with awp (he shouldn't have known he was there)
21500 - This one did it for me. He was shooting his deagle through the corner wall at the guy sitting on the boxes

So with that, my vote is perma for walls.