If you know you can always go live with your rich family, then the cost of failure is pretty close to 0, so you can repeatedly take big risks until one of them pays off.
Getting money for living expenses as you study is the life of the average middle class student in USA, he didn't say it funded Musks ventures. The emerald mine made them rich compared to other Africans, but that doesn't say much compared to the average American.
Would there be any ventures if Errol didn't fund Elon's trip to the USA? That's the point, without the emerald mining funding there would be no Elon in the USA, no Elon taking risks in ventures, etc. It can't be looked at in a vacuum of "he didn't get direct money for his ventures", it was only possible for Elon to start ventures because of the emerald mines.
I know several people who emigrated to the US with a suitcase and became millionaires. None of them had a family emerald mine, or any family wealth at all.
If you live in the USA already, why didn't you start SpaceX? Millions of immigrants come to the USA. Why didn't anyone else start SpaceX?
Anecdotal, but… I'd be willing to put the time and effort in to start a company, but I would not be willing to lose my home or fail to provide for my wife & three children in the process as neither my wife nor I have any family capable of taking us in.