Do you realize that 5.56x45 shot with MV of 2900 fps / 883 mps loses almost half of its velocity after 300 yards? Average speed on this distance is about 660 m/s then. It will take ~ 0.4 sec to hit target at this distance. So when firing at man sprinting 7 m/s sideways to you you'll need to put ~ 3 m correction ahead of him.
The video is kinda wrong, you should rather register when the hit occured, not when man visibly collapsed.