well in most jurisdictions a "no trespass" order on public land (land or places generally open to the public) must come from someone authorized to give the order, usually meaning a law enforcement officer or someone charged with administering the land. i've never known this to be some city worker.
the order must have a reasonable basis (usually unlawful or disruptive conduct, disruptive meaning behavior that goes against the purpose of the place), and it must have a clear ending date. based on what is in the news story i doubt a criminal trespass conviction would stand against this person on appeal.