Curious where you got this info from. Unlike some other countries that may have an official capital and a functional or historical capital, South Africa actually has 3 official capitals. Why not just add them all to your quizzes?
Actually South Africa doesn't have an official capital. They are all three equally "de facto" capitals. So you can say, if you want to, that South Africa doesn't have a capital, but there's no factual basis for saying that Pretoria is the only capital. You might just as well say that English is the only official language of South Africa.
You can personally believe whatever you want, but a quiz on Jetpunk has to follow Jetpunk standards. Jetpunk recognizes Bloemfontein as one of the three capitals of South Africa. If it's in the World Capitals quiz, it needs to be in your quiz.
If for whatever reason you choose not to recognize Bloemfontein as a capital of South Africa, that's your prerogative as the quiz setter. However as it's the standard on JetPunk to recognize all three cities as South African capitals, it's a little confusing and it would be nice to at least have a note about this in the quiz description, as is also normal on JetPunk when a quiz deviates from the site's standards.
In the meantime it's just frustrating and makes it look like the quiz setter forgot one.
Bujumbura hasn't been the capital of Burundi for several years.
www.britannica.com/place/South-Africa
In the meantime it's just frustrating and makes it look like the quiz setter forgot one.