795 meters is a fairly long shot but on a departing target, not particularly difficult to make. There's a host of variables that could influence the possibility of incorrect target identification, which is the defense you're proposing. Something
produced that target speed; you have a better chance of winning the lottery than proving in court that the laser conjured up the speed all on its own. At least, in 19 years of operating lasers I've never seen it done out on the road.
Before launching into all of these factors, do us both a favor and answer three questions that'll allow me to focus my response and save everyone some time: What target speed did he assign to your vehicle, how close to actual was that speed and was either of the two nearby vehicles traveling at close to that target speed? Without this information, we could waste days with pure conjecture.
Knowing this, I may be able to help you.