While the author may draw some questionable or disputable conclusions, I think he is aware that different parts of the city and different parts of NoVA look very different; it seems like it's part of the point of going for a walk to make these observations.

Is there a reason that you think Northwest is a better reflection of "DC proper"? Anacostia and Benning are very much inside the city limits- they can't represent what most of Northwest is like and vice versa Northwest can't stand in for them.