You might be rich if you funded the 529 plan with proceeds from your emerald mine. Outside of that scenario, your kids' 529 plan doesn't really have anything to do with this.
Someone with an ownership stake in a mine that produces material with a variety of industrial and commercial uses is not necessarily rich. But that person is in a relatively tiny group compared to the group containing all parents who are able to contribute to their children's educational expenses. And the "owns <part of> a mine" group's average net worth is probably a fair bit higher than that of the "can contribute to the kid's college" group.
Hence, if you own an emerald mine, you might be rich.
And if you own a failed emerald mine you might be poor. If you own an emerald mine that just barely broke even (admittedly that is a bit unlikely), you might end up middle class in the end. Of course you can also end up being obscenely wealthy from such a venture.
I don't think anyone is suggesting elon musk rose from being a homeless person to a billionaire. I guess this internet dispute is whether he made his own money, or inherieted it (e.g. like trump). Whether or not his parents owned an emerald mine doesn't really shed much light on that debate. Its entirely possible they were moderately wealthy but the emerald mine wasn't super lucrative and musk still made money mostly by means of his own combination of skill and luck.
"Regarding the so-called “emerald mine”, there is no objective evidence whatsoever that this mine ever existed. He told me that he owned a share in a mine in Zambia, and I believed him for a while, but nobody has ever seen the mine, nor are there any records of its existence." - Elon Musk, https://twitter.com/elonmusk/status/1654971702571331584
