unfortunately this teacher is correct and this is widely believed to be true. I grew up in South Africa and still have many friends over there and I was recently sent a document by a friend giving details of what is apparently going to happen upon the death of Nelson Mandella.
The plan which is translated as "night of the long knives" is rumoured to have been set in place some years ago. When Nelson Mandela's death is announced, large groups of people will descend on the white population and will murder as many of them as is possible.
It sounds hidiously far fetched as I write, but the details I read about it were horribly chilling, so if it is true it will be horrible beyond words.
South Africa, while in parts a wonderful country, has an extremely high crime rate, and the murder of white south Africans is actually not far from on a part with that of Zimbabwe, but it is not made so public. In fact I have a friend whose husband was murdered on his farm two years ago purely because he was white.
Cape town is one of the safer places to go though as it's a large tourist area and steps have been taken to fight the crime there.