Whether the cops were behaving badly is open to question. I can tell you it is almost impossible when sitting on the side of the highway at night watching traffic go by to tell the race of the driver and occupants. Between the lights in your face and the pace of activity, seeing who or how many are in a car is very difficult.
He probably ran his plates before he pulled him over and saw who he was and might have recognized him then. You never know who you could catch driving home drunk!