I don’t know what actions Mandela took, I’m afraid. I only know that he spent 25 years in jail, and that his side won the political battle in the end of the day. Africa now lives with the consequences of that victory, and it seems a Pyrrhic one at best.
A terrorist is hard to define. Israel pushed out the Brits using terrorist tactics, and the terrorists became the leaders of the new country.
A terrorist is surely someone who kills in a hopeless cause. If they ever win their battles as did Mandela, they become the new leaders and can re-write the history books. The ‘terrorist’ retrospectively becomes the freedom fighter.
If South Africa descends into complete disorder and has to go through another revolution, Mandela might become a ‘terrorist’ once more. Those in power will as usual define the politically correct terminology.