“Luck Is What Happens When Preparation Meets Opportunity" -Lucius Seneca (Roman Stoic Philosopher)
What is being argued is that they where lucky to be born in a society where their skills could make them millions.
I.e. they didn't create all those money in isolation, they made them in a system that made it possible.
Thats the point. Not that they aren't brilliant at what they do. Just that no one in that end of the wealth scale is that brilliant that they created purely based on their own skills.
Again, not taking anything away from Buffett, just pointing out that luck is a really big deal that doesn't get much air time.