Don't be hung up on ranks. I learn TKD/MMA that has Hapkido blended in and he is a 3rd Dan ... goes for 4th on Saturday. From talking to him he says anything over 3rd gets very political. A person at this rank does not necessarily have to been even learning his own art to get this just as long as they are doing "a" martial art and have put in the required amount of hours.
Possible this instructor is not unlike mine that has spent a tremendous amount of time at this rank and just hadn't seen it as necessary to get the next Dan because teaching was far more important.