I doubt he would have called the police. I know you were shaken up but something to keep in mind if it happens again is that you can call their bluff. Just say, "Ok, lets wait here for the police, I'm sure they will be interested in my report of your dangerous driving." Say it with a straight face and serious voice and you will probably see the guy huff and puff and get out of their as fast as he can.
And if they do call the police then you get to inform them of the dangerous tailgating. Also, a camera might not be a bad idea in Japan anyway. From what I have understood previously traffic related accidents can be "messy" in the legal sense and having a video available showing what happened might be a big benefit.