Eh, pretty sure Musk can also be stubborn or denialist in the face of some facts. He is trolling because he has no intention to follow suit regardless of evidence.
"both sides" has been such a demonized lens that it's like we're purging the idea from our brains, legitimately both have a point here
yes it's easy for musk to renege or move the goalposts
yes it's also easy to say "we can solve this fundamental survival issue for only 6 billion" without a real plan in place taking into account all the logistics
I really don't think you can solve it with such a simple number, heck I don't think the
progress you'd make spending that much would lead to long lasting change...I think the organization he challenged had 4 billion last year? and they didn't fucking 66% solve world hunger

but what will happen is the people he challenges will say "no we're not playing that game" and he'll say "see? they can't" and both of them will have their cheerleaders thinking they won