Are University Graduated WEIRD people psychologically different to Generally Educated WEIRD people?
A lot of psychological research takes place in societies that are Western, Democratic, and Industrialized, and that from a global/historical perspective are relatively Educated and Rich.
Of course, within those societies, people vary in their level of education and their socioeconomic status (e.g., wealth, income, financial security, earning potential, etc.).
And education and socioeconomic status have numerous correlates with psychological variables and life outcomes.
E.g., educational attainment is positively correlated with life time income, intelligence, and political views.
There are two obvious explanations for these processes:

Education changes a person. They acquire general and discipline specific skills. They get exposed to different experiences, career opportunities and so on.
Psychological characteristics predict interest, access, and success in higher education. For instance, more intelligent people are more likely to be granted access and succeed in higher education.
Third variables. Factors like family socioeconomic status predict psychological characteristics as well as the probability of pursuing higher education.