and we know that there is a causal relationship between academic achievement and progressive politics
Do we know that? That's actually a very strong claim, significantly stronger than the OP's claim of correlation. For a comment about skepticism of statistical links, your rebuttal is more problematic than the original claim.
But was causality established? That's a very difficult thing to do. I'd like to read the paper if you can find it.
Because it's just as plausible that people predisposed to think critically are more likely to both go to college and move left politically in early adulthood.