I think I can explain what's going on here...
When Google tries to determine which state you're in, it uses your IP address, and doesn't ask you to confirm. This basically means that, if you're using a VPN or proxy(for work, say), and it's based out of DC, Google will pick you up as being there, whether you're in DC, Mississippi or Rhode Island.
I believe that's correct, and with a sample size that small, it matters. They're likely picking up government workers, lobbyists and tourists visiting DC/staying at DC hotels.
