[Hebrews 11:6]

If I'm not mistaken, in most jurisdictions it is indeed a crime not to obey a peace officer's lawful order during an emergency. Thus, if a riot is already occurring, does an officer have the right to order a citizen's assistance in a limited way?

You overstate the case. The officer was not asking him to quell a riot, a task which might include physical or even armed intervention. He asked him simply to help discourage a riot by sending a message, in this case electronically.

[OldDeckHand]

'He asked him simply to help discourage a riot by sending a message, in this case electronically. "

Then, using your logic, cannot the federal authorities compell Rush Limbaugh or Glenn Beck to instruct their listening audience to not act in a violent way.

Yes, I did overstate the case - intentionally. There wasn't a riot taking place. There was just a collection of, at best, emotionally anxious teeny-boppers. How is that an emergency? If that's an emergency, virtually anything is an emergency, and then the powers of the police-state become unlimited.

[Jack Hydrazine]

The guy wasn’t asked. If he was asked by the police and he refused then they could not have arrested him. Since he was told (ordered) by the police to do so he was not obeying.

Being told and being asked are two different animals altogether.