I don't really get what your interviewer was trying to say...it's DC, so literally over 99% of students they interview are "out of state." Not to mention, interviewers at Gtown don't have your stats during the interview, so I don't know why yours would have told you to expect to get waitlisted because you were a good applicant from out of state. The majority of their class comes from the Northeast and California, where there are good state schools, and while they are definitely concerned about losing students they accept to their state schools, they still have to offer at least some acceptances.
That being said, they do get 11k+ apps, so they really scout out the people who actually want to be there, and people who express that in the interview (or send an LOI if waitlisted) up their chances significantly of getting in. Good luck 🙂!