I think people have always associated a college degree with higher intelligence. When I was young, college was something that you did if you wanted to become an engineer, or a doctor, and other professions that required a lot of extra schooling and subjects like advanced math or biology. So it was a simple association- if you went to college, you were smart.
Like any stereotype, there will be rules and exceptions. For a JW, higher education was something that we were asked to forego in order to keep our faith strong. While this normally might cause people to have an inferiority complex, we also understood that we were smarter for doing so, since we would enjoy salvation while those 'smarter' people died at Armageddon. So we had this ironic situation, where we passed on higher education while feeling superior to those who chose to go to college.
As for me, I was a good JW and passed on going to college. I became an IT technician and an IT administrator for a while. I only got the most basic certifications, and I did so around 20 years late, mostly so I could get a raise.