No. It's strictly because of travel time from the "observed spot" to the camera. He explains it in the back half of the video, but for his setup (and every camera everywhere, including your eyes!), it doesn't matter just how long light took to get to the point where it scatters, but also how long it takes for it to get from that point to the detector. If the camera is placed far enough to the side, that time delay is close enough to identical for all samples, but if the camera is in line with the laser, there is a substantial time difference for light scattering close to the camera to light scattering near the far wall.