Smart motorway camera flash

[Dog Star]

Had a curious incident this morning - I was in the smart controlled section of the M62, gantries showing 50. I was in the leftmost lane of 4 and doing bang on 50, as was the car in front. And the truck on the right. In fact all 4 lanes were doing the same speed. One of the cameras flashed - no idea which one, however I cannot see why as nobody was speeding.

Cool starry bra, etc, but what's all that about?