Being a native Washingtonian, I often hear from people that I am the first native that they have met. On a tangent - I also get asked, usually by locals (either native, or with enough seniority), what part of DC and they often respond, "Oh the actual city." It used to bug me that people said they were from DC when they weren't. Until a high school friend went to college in Indiana. After spending a good part of the first month trying to explain to people where Maryland was (no it's below New York, no, above Florida, no it's not near Wisconsin), she gave up and started saying she was from DC. Because if people don't know where DC is, well, they don't ask. Or so it seems.
So, back to the native point. So, in a book that takes place primarily in Alexandria, VA, it would not surprise me to have a character state that they grew up in DC and have someone respond that that was unusual. Unless - the person who responded was from DC themselves. And they were sitting with a third person who grew up in Alexandria (which ,you know, was part of DC originally). Because those of us who grew up here know pother people who grew up here. Sure some of them left, some of them later came back, but some of them are still here. As anyone who grew up here would know.