People have a funny way to look at how violent a transition and especially leaders are or aren't depending on whether they agree with the outcome.
The ANC ... well ... in the words of the Apartheid museum [1] (ie. The South African government's own words):
"Demonstrations against the killings followed in many parts of the country and led to the banning of the main African opposition organisations, the African national Congress (ANC) and the Pan Africanist Congress (PAC). Both went underground, and formed armed wings, Umkhonto we Sizwe (ANC) and Poqo (PAC)."
Yes, Nelson Mandela ... founded a revolutionary army. Yes, I agree with the outcome too, and the process was almost bafflingly well executed. Bombings, placing landmines on public roads, kidnapping and torture were some of the tactics used. Again, bonus points for the outcome, and for successfully keeping control of this army after it was no longer needed, but peaceful ? Please. Also, I would further argue that South Africa did not exactly become a haven of peaceful coexistence under Nelson Mandela.
India, and Gandhi is another example of this. So is Che Guevara. Looking how peaceful what happened with them at the helm of organisations is, you really, really, really wonder why these people are considered nonviolent.
Yes, Gandhi thought (and taught) that violence was beneath him, but he certainly had the option to act and prevent the people he led from using violence. What happened ... he sent out his forces and the opposing side sent out it's forces, and at least 10 million died. Granted, not during the revolution he was famous for, but he was in command during the partition wars. Doing India's independence he was not peaceful either. He commanded forces that, time and time again, attacked others.
And Che Guevara. He was not a violent man, you see, he simply saw the bourgeoisie as constantly committing violence upon everyone and he was just using the minimum amount of force to prevent them from continuing that. That minimum amount of force, of course, included things like shooting any medical doctors on sight, several massacres, and having his followers do worse than even that.
Plenty more along these lines, Kemal Ataturk, the French revolutionaries, the Communists (granted, not so much in the USA, but even in the USA the "real socialists" are peaceful), muhammad, the muslim prophet, ...
But men of peace ! Men of the people ! In reality, living with some of these men was like living as a Jew under Hitler. Ironically, Adolf Hitler is also a Nobel Peace prize laureate.
[1] https://www.apartheidmuseum.org/turn-violence