Earlier quoted context omitted.
https://en.wikipedia.org/wiki/Srinivasa_Ramanujan
The exception that proves the rule.
https://en.wikipedia.org/wiki/Albert_Einstein
https://en.wikipedia.org/wiki/René_Descartes
https://en.wikipedia.org/wiki/John_Forbes_Nash_Jr.
https://en.wikipedia.org/wiki/Alan_Turing
https://en.wikipedia.org/wiki/David_Hilbert
I think this rule is just wrong. Some mathematicians come from privilege, some do not. Even for the ones who do, it's rare that they come from _great_ privilege for the time. They are the children of mayors, not kings -- professors and engineers, not the financial aristocracy.