The opposite of being "were unoccupied" is "were occupied." When something is unoccupied, it means that it is vacant, empty, or not being used. Conversely, when something is occupied, it is being used, filled, or inhabited. For example, a house that is unoccupied is vacant, but when someone moves in and inhabits it, it becomes occupied. Similarly, a parking space that is unoccupied is not being used, but when a car is parked in it, it becomes occupied. Overall, the antonym of "were unoccupied" is "were occupied," indicating that something was being used or inhabited by someone or something.