Notice how Haaretz tries to avoid the subject by first reporting the story this way:-

Mandela received weapons training from Mossad agents in Ethiopia ||| Top-secret archive document also reveals that Mandela was 'familiar with the problems of Jewry and of Israel' and that Israeli operatives tried to 'make him a Zionist. 'Nelson Mandela, the former South African leader who died earlier this month, was trained in weaponry and sabotage by Mossad operatives in 1962, a few months before he was arrested in South Africa. During his training, Mandela expressed interest in the methods of the Haganah pre-state underground...

But later on down there we read:-

.... In January 1962, he secretly and illegally fled South Africa and visited various African countries, including Ethiopia, Algeria, Egypt and Ghana. His goal was to meet with the leaders of African countries and garner financial and military support for the armed wing of the underground African National Congress.

A letter sent from the Mossad to the Foreign Ministry in Jerusalem reveals that Mandela underwent military training by Mossad operatives in Ethiopia during this period. These operatives were unaware of Mandela’s true identity. The letter, classified top secret, was dated October 11, 1962 – about two months after Mandela was arrested in South Africa, shortly after his return to the country.
“As you may recall, three months ago we discussed the case of a trainee who arrived at the [Israeli] embassy in Ethiopia by the name of David Mobsari who came from Rhodesia,” the letter said. “The aforementioned received training from the Ethiopians [Israeli embassy staff, almost certainly Mossad agents] in judo, sabotage and weaponry.” The phrase “the Ethiopians” was apparently a code name for Mossad operatives working in Ethiopia.

The letter also noted that the subject in question “showed an interest in the methods of the Haganah and other Israeli underground movements. “It added that “he greeted our men with ‘Shalom’, was familiar with the problems of Jewry and of Israel, and gave the impression of being an intellectual. The staff tried to make him into a Zionist,” the Mossad operative wrote...

I did quote this earlier:

Chairman of the South African Zionist Federation Avrom Krengel said in a statement...that former Israeli Prime Minister Menachem Begin had been a major influence of Mandela's. "The strength he drew from Zionism came from Menachem Begin’s book which inspired him to initiate the creation of Umkonto We Siswe. In turn, people across the world drew inspiration from him and his amazing ability to draw people together."

And more background, from Lary Derfner:

In Chapter 42 of his autobiography “Long Walk to Freedom,” Nelson Mandela describes how, in 1961, he began forming the African National Congress’ (ANC) military wing to launch guerrilla attacks on the apartheid regime. “I, who had never been a soldier, who had never fought in battle, who had never fired a gun at an enemy, had been given the task of starting an army. … I began in the only way I knew how, by reading and talking to experts.”
...He mentions three books that were crucial to his education. One was Commando by Deneys Reitz about the Boer rebellion. The second was Edgar Snow’s Red Star Over China about Mao’s revolution. And this was the third:
'I read The Revolt by Menachem Begin and was encouraged by the fact that the Israeli leader had led a guerrilla force in a country with neither mountains nor forests, a situation similar to our own.'...