Sometimes he looks at the floor where the doorway is below and then adjust his play to engage someone coming from there - could just be reacting to sound cues we can't really tell but it does raise suspicion of a wallhack at times, also couple of times staying dead center mass on a player while not aiming down sights which is quite hard to do without an aimbot but again due to low quality of the video can't be entirely sure. Without playing against him to get a feel for it or a better quality video I'd go with it being someone whos spent a lot of time practising their camping skills.