I don't know if it's as simple as it being always being either causation or correlation. Education level is used as a proxy of potential wellbeing indicators.

Yes, there are rare people who have never finished high school and had material success, probably most drug dealers who cashed out and bought franchises or real estate. So logically then general causation is ruled out.

But for most people without high school degrees it's extremely difficult to disassociate their lack of education with later material success.