In the video, beginning at 1:03, he pulls into the right lane. As he passes on the right, he looks out his window back at the driver. It appears that he then slows down to get next to her car, but slowed down a bit too much, so he sped up to catch up, just to flip her the bird.
Of course, none of us were there. I could be wrong.
Looks to me as if she sped up. Could be wrong, but given the prior controlling behavior and the apparent desire to provoke other drivers into hit-worthy YouTube videos, it stands to reason.