I don't know which is the size of those regions, but I think it wouldn't be so weird a whole region had higher population than a city. I mean, a well-sized rural region should hold many villages and small towns which, in sum, could reach a higher population than a single city.
Though the amplitude of the disparity is surprising, Heen is a pretty small city over a very small territory, whereas Eykfar is a much larger region.
That's still a pretty big difference, though.
