An opinion piece is not a source. Where did they come by this data? Following the links only takes this far: https://cdn.ramseysolutions.net/media/company/pr/everyday-millionaires-research/national-study-of-millionaire-new.pdf

Which 1) Indicates it was a survey. I'm sure millionaires like to believe, and have other believe, they made it all themselves but that's hardly scientific. They conveniently forget things like daddy paying to get them into a fancy school and giving them a cushy position in a business they own.
and 2) doesn't share the study or methodology in any way. It is impossible to check their work.

So we just have the word of a company that wants your money saying "trust me." They also have a bridge they would like to sell you.