Remember these are people who know what it's like to go through apartheid and ethnic cleansing.
South Africa today is largely governed by the people who fought and won against apartheid, so it's understandable that they feel a level of solidarity with the people of Palestine.
(in this context I'm choosing to gloss over the real and present issues with the ANC, because they are not relevant to Israel's genocide)
He sounds similar to those insufferable effective altruists. Most of these people have a genuine skill in something narrow, and the willingness to walk all over everyone in pursuit of the 'highest score' achievement on their 'net worth'.
Yet they've convinced themselves that only they can save the world, so they have to make as much money as possible by any means necessary in order to fund misguided charities. They'll burn down the planet and anyone necessary to make money so they can save it.
Sir Chris is still in control of his charity, so really all that money he gave them is still in pursuit of his own goals, the charity is only spending money it makes through its investments. So whilst it sounds so generous to donate billions to charity and I'm sure it brought him great publicity, it's little more than a tax-efficient way to attempt to bring about societal changes that society didn't ask for.
I'm sure it was also nice that whilst he 'donated' billions to the charity, when it came to his divorce settlement, that was taken out of his 'personal fortune' which amounted to less than a billion.
So don't give him that much credit.