Sounds like he was having a bad day and was being an impatient douchebag.
About 8 months ago, my son and a neighborhood girl had a carpool arrangement. It was a Friday afternoon and my son was going home with a friend, so it was just me and the girl driving home. We don't get a ton of traffic in my area but it's certainly heavier at ~4pm on a Friday afternoon than usual.
While stopped at a red light, I saw a guy in my rear view basically using the turn lane behind me as a passing lane to get ahead of several stopped cars. After the light turned green, I kept an eye on him in my rear view and he kept weaving in and out of traffic behind me. I was in the left lane and he passed me on the right, then darted in front of me missing me by inches and causing me to slam my brakes. Apparently he cared less about his early 90s black Geo Metro than I did for my car. I flashed my lights at him (no hand gestures with the young lady in the car), and this apparently sent him into a road rage fury.
Over the next 2 or 3 miles, now that he was in front of me, he kept flipping me off and brake checking me. I was tolerating him surprisingly well, and finally got an opportunity to quickly pass him on the right and get ahead of him. He continued to flip me off in my rear view but I really didn't care at this point. Then I guess his destination approached because he got into the left turn lane, drove next to me for a few hundred feet, leaned over to his passenger side and gave me the middle finger salute before finally turning left. What surprised me most was that it was a guy with a gray pony tail, probably early 50s, and not a young kid. I pointed and laughed at him for as long as he could see.
Fast forward a few months and I'm on the same street but about 6 or 8 miles closer to my house. Lo and behold I see the same black Geo Metro turning into a local restaurant. Free from my burden of being a model citizen in front of our carpooler, I turned in behind him and pulled up beside him in the parking lot. When he got out of the car, I noticed he was no more than about 5'4" and 130 pounds. I got out and asked if he remembered our encounter, but he assured me it wasn't him. I told him he must have a gray haired, pony tailed, shitbox driving doppleganger in the area and gave him another opportunity to tell me whatever he was trying to tell me back then when I was unable to discuss the situation but he refused. I told him to be a little more careful out there and left.
So yeah, there are some impatient hotheaded douchebags out there. Maybe you'll get the opportunity to see him in a few months.