This is a very interesting question, and it's one that has been debated for a while now. How much does kwaito owe to American hip hop and rap music, if anything? You'll find people who could argue it either way, and some do, but the most reasonable position is that kwaito exists as both. Culture and cultural expressions are often the result of many forces meeting, and in our "global" world today, few things are as simple as they seem.
Kwaito is to its South African fans a very similar phenomenon as rap music is to its fans in the US. Both share urban origins and are often infused with political or social commentary. Kwaito, to a degree, is popular because it requires no formal musical training and can be created by people with limited access to musical instruments. Rap is similar in this respect. Though many rap albums now feature complex production values, its origins were found on street-corners and inside of clubs.
As for themes, how could the creation of music not be an expression of democratic freedom? The ability to simply create original music without interference represents that anywhere in the world. It doesn't have to always be about politics and cultural change. Kwaito can be fun as well in the same way that rap and hip-hop music can be. If all the music were simply created to reflect politics it would be pretty dull.
As with rap, the lyrics involved in kwaito can be hard to figure out. This is another reason why people might simply label it as a "rap clone." The reality, though, is that many of the lyrics represent deeply held beliefs and messages of social change. It's a matter of how much effort you put into understanding them, and how much you understand about the South African culture to help make the links.
In short, kwaito does share roots, intended or otherwise, with American rap music. It is not, thought, a clone. It is an organic expression of the local culture and just as complex, thematically, as any other form of musical expression. It is both an expression of freedom and a version of "rap in another language." The important part to remember is that they are complimentary cousins, not rivals or copycats.