Well you are supposed to leave a 2 second gap, which is what you had until he pulled in, after that it is a very short gap. How big is the gap? (count the frames and divide by 30 or 60fps.) He also didn't indicate soon enough, supposed to be 3 or more flashes before starting to move.
Doesn't look too bad on the wide angle video, even for us that are used to wide angle. Given that we can see the A pillars on both sides your dashcam must be wider angle than most - you should zoom it in a bit so that it looks like you experienced it, then you would get a different response...