In this particular case I agree with you. But how would you write this into a law that citizens and police can reference to determine whether a particular action is ok or not?
If the issue is a person removing a piece of tape covering a license plate, then really nothing happened. The citizen unobscured state property which is supposed to be visible. It would be like removing a sticker from a speed limit sign, or picking up litter.
If it's some other piece of plastic attached to the car itself, well IMO that's what courts are for. That cyclist goes before a judge and maybe some technical reading of the law interprets what he did as tampering with the vehicle. Another completely reasonable interpretation though is that the cyclist was making the shared roadway that the car was on safer for everyone else.