I spoke with Michael Zierler yesterday to get some answers about the curfew, since he was (maybe "is," I'm not certain) acting as public information officer.
The resolution's intent was twofold, he told me.
First was to prevent people from being out in potentially dangerous conditions because they were curious. "You can stand outside your house," Michael told me, but "nobody should be out just to see what's going on outside."
The village and town wanted emergency services personnel to be able to focus on things like downed trees and flooding, instead of people "intentionally swimming in the river or accidentally driving through flood areas," Michael offered as examples.
Likewise, the curfew was to keep the streets clear for essential emergency vehicles. "The entire personnel had been working for 16 hours already," Michael told me, and empty streets removed both a distraction and a potential delay in the form of vehicles.
Police advised downtown businesses to close, and rode up and down the streets announcing the curfew over their speakers. Notifications were spread via social media, local access cable, municipal websites, and over the phone to anyone who called any town or village office.
There was also a countywide ban on driving, Michael said, although New Paltz police were not stopping people "just for driving." No checkpoints were set up to stop drivers.
Another underlying concern was the fact that it was impossible to assess roads for damage. West of the Wallkill, where they won't be checked until the bridge is passable again, there's still a travel ban to the best of my knowledge.