This is Musk trolling the "tax the rich" people. We've all seen these unfounded claims/memes running around that "world poverty could be solved by blah, blah, blah". He's just asking them to put his money where their mouths are. Show him the evidence and he'll fund it. Don't have any evidence to back up your claim, then fuck off.
If they don't have the evidence, then they are just contributing to the fake news epidemic that currently causes most problems in the world.
In fairness to the UN dude, he never actually said he could solve world hunger, he said that cash would save a bunch of peoples lives and also offset some of the things-got-even-worseness of covid.
CNN added the "2% OF MUSKS WORTH WOULD SOLVE WORLD HUNGER" nonsense to get people to click on the article.
Which doesn't exactly refute your issue with 'fake news' I realise, but...