Microwave radars measure the strongest vehicle reflection, not always the closest vehicle. Microwave radars have sensitive receivers, nearby transmitters and high power sources can induce false signals and false speed readings. Moving mode radar has multiple sources for incorrect speed readings that depends on traffic close to the radar and reflective stationary objects, like guardrails, close to the radar.
Lidars can produce a false reading if the target vehicle is greater than about 500 feet. At closer ranges the narrow beam must be aimed at the same vehicle surface or risk a speed error from 1 to 25 mph. Additionally lidars will produce a false speed reading by scanning the ground, no moving targets required.
The Police Radar Handbook, released March 2013, has the answers as to why you might have received that undeserved citation. The book explains proper radar and lidar use, and results of improper use. In many instances errors are predictable knowing just the general setup.