Allowing a dog sniff to be reasonable suspicion is what is strange. But unfortunately it is. If you are stopped, such that the police dog can sniff your car, then they can sniff your car. But the cops can't stop you just to let the dog sniff, without more suspicion. Since the car is stopped for a traffic stop, it gives a chance for the dog to go work. Put it another way, the cop is standing on the side of a road near a traffic light. If the car is stopped at the light, the dog can sniff away. But the cop can't stop you, or hold you longer than the light.