I believe a good portion of the first floor is actually garage. As I understand, in addition to the garage, there is one bedroom and bathroom down there that wasn't shown. So, unless your room is on the first floor, you need to go upstairs for all of the other living space. So, kitchen, dining area and family area plus 2 bedrooms and 2 full baths are upstairs.
In the DC area, town houses are common and often when the town house has a garage, it is basically the first floor. Then there are generally two more floors on top of the garage, so you walk upstairs to the main living area on