Probably lots of ways to contest such a ticket.

Bikes aren't required to have speedometers.
Speed limit not conspicuously posted*.
Bicycle speedometers do not have any standard of accuracy.
Etc.

(*=Since the MUP is not an actual vehicle roadway, not only would there need to be signs specifying a speed limit, but also stating what the penalty would be for exceeding that limit, since for activities that do not require a license, there is no contract of agreement or expectation that ignoring a rule will carry a penalty)

And the sad thing is, while the muggers and burglars roam free, some poor slob is going to have to waste his time in court fighting such BS- all because harmless white guys on bicycles typically pay their fines and pose no threat to the donut-eaters- while the muggers get public defenders and just do a stint in the $50K-a-year barred hotel instead of paying fines.