The place is described fairly accurately and it indeed private--separate entrance and ability to move in and out without feeling like you're in someone else's space. It's well-stocked and mostly quite clean. The bedroom with the queen bed is a very good size. I think it would comfortably fit four adults in the entire unit before feeling like things were really cramped. There are some signs that it needs a little TLC (peeling paint in the bathroom, for example). You can tell it's being used for lots of guests. As others have mentioned, you can hear the movement of the people and the dog whenever they're upstairs and the bathroom is indeed very small, although very good water pressure. The communication from the owners was straightforward and clear, which was appreciated.
Worth noting: we rented this place because it's pet-friendly and we needed somewhere to stay with our cats for a couple of days while our home was painted. Be aware that if you bring a pet, they charge a pet fee that I can't find listed anywhere in the fees or description. It's not outrageous, but it's a factor. Additionally, there is a locked closet that contains a great deal of roach poison: something our cats could access by swiping under the door. Luckily we noticed before it became an issue. Do a full sweep of the place when you arrive if you're bringing pets (something most pet owners would likely do anyway, but worth the awareness).
If you're paying for the parking, the picture used in the listing is no longer accurate, as there's not currently a garage door to secure the parking area. The listing notes that parking is secure and there's a photo of the garage door, so updating the listing would allow guests to truly understand what they're paying for. While the parking is off-street, as a fellow DC resident, I don't trust leaving my car accessible in an alley if I can help it because I've dealt with too many car break-ins over time.