The charge could very well be bogus as many of my student clients get charged just because police have a tendency to charge everyone involved. For example, if someone gets jumped and is defending themselves, the police generally charge everyone involved and let the judicial system sort it all out. Really no point in jumping to conclusions until all of the the facts are out. Here is the statute which makes it a simple misdemeanor to do a variety of things:
723.4 Disorderly conduct.
A person commits a simple misdemeanor when the person does any of the following:
1. Engages in fighting or violent behavior in any public place or in or near any lawful assembly of persons, provided, that participants in athletic contests may engage in such conduct which is reasonably related to that sport.
2. Makes loud and raucous noise in the vicinity of any residence or public building which causes unreasonable distress to the occupants thereof.
3. Directs abusive epithets or makes any threatening gesture which the person knows or reasonably should know is likely to provoke a violent reaction by another.
4. Without lawful authority or color of authority, the person disturbs any lawful assembly or meeting of persons by conduct intended to disrupt the meeting or assembly.
5. By words or action, initiates or circulates a report or warning of fire, epidemic, or other catastrophe, knowing such report to be false or such warning to be baseless.