In my experience, motorists at night have no freaking clue what the hell they are seeing when coming up on a bunch of blinking lights. It's most likely that the motorist was trying to figure our what you were and fixated on you, slowed, figured it out and then carried on. If you were completely dark, they would not have seen you at all and probably would not have buzzed you.
If there was a standard lighting system on bikes, drivers could/would get used to them. Random lights of different styles and random placements (seat, helmet, body, etc...), make it hard to figure out distance and the speed you are traveling.
I live near Lancaster PA, where the Amish ride scooters at all hours of the night and in crazy fog and snowstorms. They wear a blinking vest that is crazy bright and now that I have seen that vest on a few guys, I know right away to steer clear and give them room.