Cop was tagging the civic and saw you behind him. Based on his observations you were going the same speed, as like cossey said if he did not see the civic pulling away from you, then you guys are going to same speed.
Cops are trained to judge speed with more then just a radar/laser, using points of refrence and a watch, plus teh common sense that if you tag one car going XXMPH and the car behidn it is not falling back then the car is also going the same speed as in your case.
Gotta clam down with cops, swearing/cussing getting angry and showing attitude does not help your situation one bit. You may get it dropped down to something less severe, but doubt your going to walk away 100% clean on this one unless the judge doesnt like the cop that ticked you :lol