I do mean it that way. I am honestly tired of people who think they are cool because they live in Sofia (because they imply the others are not cool because they do not live in Sofia). It turns personal for which I am sorry, but it is still personal.
The population of Sofia as a proportion of the population of Bulgaria is 1,449,277/7,606,000=0.190543913 which is roughly 1/5.
The "more than one third of the population of Bulgaria" is a typical "we are so cool" distortion of the truth for the Sofians...