Sorry but perhaps I not have seen good, but where see wallhack??
I do believe that its on the 1:50min mark onwards.
Before that time is hard to say because of the UAV.
When he started to throw grenades, he had no UAV or spotting over that area.
But, now that I think better of this and watch the video again, he could know that there was a sniper around there.
If it was my call, I would wait until another video gets posted, a more "specific" one.
Btw, was this on the vanilla NRNS server?