For the South African cities I think you need to define what you see as a city. Soshanguve is a township but is part of Pretoria and has been since at least 1994. Yet Soweto, which is a township of Johannesburg and has about 3 million residents, does not make the list. Same issue with Evaton, and most of the cities that form up the Ekurhuleni metro exceed 500 000 residents yet neither they nor Ekurhuleni make the list. If a South Africa cannot get 7 out of 7 what chance do other nationalities have?
In this quiz we are going by the "urban area" definitions as per citypopulation.de. I agree that the definitions are a bit dubious for cities in Gauteng as they follow urban area limits as opposed to administrative borders, but this is more in line with common JetPunk standards for urban areas/cities.