I doubt if the police witnessed this. They would have came over and checked out what was happening.
If you really aren't a law student playing with us though, aren't you concerned to have this up on the net?
Do not, under any circumstances, admit to any of the charges in the complaint. If you do, you are screwed. The State has to prove its case beyond a reasonable doubt. Was it dark out? Where was the witness standing? What did he see in your hand, exactly? How is he sure you simply weren't saying "hi?" Heck, maybe you waved to show the boy you were not armed, and your hand wasn't on your hip, but instead you were scratching your butt. [Save these angles for the trial, not the pre-trial hearing--in the pre-trial hearing, all you simply have to say to the prosecutor is "are you convinced that I wasn't doing something else?" If the prosecutor responds, "Well, what were you doing?" reply "I could have been doing practically anything"].
Furthermore, any error on the complaint is significant and the complaint should be tossed. Do not acknowledge to the cops that the complaint is invalid. Let them find out for themselves when the judge dismisses the case. The first words out of your mouth to the judge should be, "Good Day, your Honor. I tried to do some research on my case before coming in today, and I believe the complaint is incorrect."
You are entitled to a pre-trial conference with the prosecutor. Again, admit to nothing but being there that evening. The prosecutor must lay-out his case to you before the trial begins. If the prosecutor is a hard-ass and insists that your pre-trial meeting occur right before the trial do the above, and when your case is called, inform the judge: "Your Honor, I request a continuance because the State has only now presented me with its evidence against me and I wish to speak with an attorney."
Do not, DO NOT admit anything. If the prosecutor or the judge try to pull some crap along the line of "Mr. BMS, if you simply acknowledge that you did what the "witness" claims you did, we can take care of this matter without re-scheduling another hearing," respond "With all respect (not 'all due respect,' sorry, pet peeve), your Honor, I cannot answer that question without consulting with an attorney." If someone presses, reply "I cannot answer any further questions."
Did I mention that you should not admit to anything?