Well, living in New England and knowing our - my city's, anyway, winter parking ban, I would say having your car parked where you know nighttime parking is restricted, between midnight and 6 AM, means you violated the sign/law.
eta: I see the son was parked in a (presumably private) parking lot. All bets are off. 'Overnight' is whatever the owner of the lot says it is.
See even this changes by area. In my town in winter you can't park on the streets any time after dark. I'm not sure why since I would think a storm starting at noon would have just as much of an issue with cars on the street for plowing as a storm starting at midnight!