First of all, while it is true that blacks had almost no freedom in SA, they didn't have a whole lot of freedom anywhere else in Africa either. If you look at some of these maps, and at the one from the 70s in particular, there was not a single multiparty democracy in the whole of Africa, with the exception of Botswana, which is one of the most prosperous and corruption-free countries in Africa. And these are just the countries that don't even make a pretense of being democracies; as you can see from the 1987 map, Egypt and Sudan were classified as being multiparty democracies, even though in practice they definitely weren't.

I can't tell you for sure whether the citizens of other countries in Africa had as few rights as they did in SA, but nonetheless one shouldn't assume that there were a whole load of other free countries in Africa to compare SA to.