Very similar to the situation in North Boston when they were looking for the Marathon bombers. People were ordered to hunker down in their own homes while the police were seeking the bombers. It's actually a protection order intended to keep ordinary citizens from being confused with the miscreants.

Police and NG have always had authority to restrict movement during extraordinary situations like the looting after Katrina but those extraordinary situations have (as far as I know) been somewhat loosely defined. It's very hard to be prescriptive on things you can't anticipate. I suspect the pepper pods are technically within their authorities during a situation like that but a bad idea (and certainly bad optics).

In general, I think it's better to consider these situations from a time-phased approach and let the situation unfold. If authorities are abusing or misusing their power, that will generally become very clear over time and the citizenry can respond appropriately. Decisions can be considered and debated after the fact and policy adjusted for the future but hamstringing authorities when they must take time-critical actions to prevent general harm (like the wanton destruction of irreplaceable artifacts) is a bad idea.