Flashed

I was driving on a 30 m.p.h. road this morning at my usual speed (somewhere between 31 and 33), and the car behind me actually flashed his lights at me the way you do when someone is in the left lane on a highway, and you want him to get over to a slower lane. The problem is that there was no other lane. I'm not quite sure what he expected. This is the first time someone has ever flashed me on a one-lane road.