When I was pulled, the police officer asked me a funny question "Why didn't you slow down when you saw me?" Seemed like a strange question to ask me (and I didn't get into a debate because my 5 year old was in the car) and I stumbled on that. My response was just to say, "I guess I must have been speeding, sir, so I'll take that ticket."
Cops ask you questions like that to try to get you to admit guilt, which it seems you admitted as a possibility. I'd still fight it though; seems you have a good case.
If a cop asks you if you know why he or she pulled you over, I think it's best to say you don't know. Unless you obviously did something stupid, because then it may just piss them off.
Yup, the old "Do you know how fast you were going?" game.
Now, let's say you were doing 75 in a 55. You know you're speeding and you get pulled over.
Officer asks, "Do you know how fast you were going?"
You think admitting to knowing you were doing 20 over might be a bit dumb, so you play a little bit of a bargaining game. You say 65. Well, regardless of what he actually clocked you at, you've just admitted to breaking the law. So, now he can much more safely tell you that you were doing 75, but he's going to let you off on just a ticket for 10mph over. This way if you contest the ticket, he only has to show up to court and tell the judge you admitted to it.
Sometimes the best thing to do when pulled over is to preempt any questions with your own. As an officer approaches your car, put the window down halfway, turn the interior dome lights on if it is dark out, and put your hands on the wheel, then just ask "Is there a problem officer?".
Anyway, good luck on contesting it, let us know how it goes.