" A laser gun projects a short pulse of invisible, intense, infrared laser light (as opposed to radar microwaves) at a specific vehicle. In order to measure the speed of the vehicle the gun uses the known speed of light to determine the range of the target by timing the flight if the pulse from the gun to the vehicle and back. By taking a series of ranges over a known time, normally just a few nanoseconds, and comparing the distance the target has travelled between the pulses, the speed of the vehicle can be determined. Although the laser beam is relatively narrow in comparison with radar beams it can still scatter due to atmospheric conditions and reflections. "
Given it is a narrow beam device it seems unlikley the wrong vehicle was hit.
As the site Falchoon quoted said" The speed cameras used in the ACT are laser operated speed measuring devices that are extremely accurate. The speed cameras are certified as being correct at regular intervals, so that certification can be produced in any subsequent Court matters. The speed cameras are only able to target one vehicle at a time. "
Good luck but my money's with the cops.