In that op-ed, Michael Mann writes:
"Nate Silver was trained in the Chicago school of Economics, famously characterized by its philosophy of free market fundamentalism. In addition to courses from Milton Friedman, Nate might very well have taken a course from University of Chicago economist Steven Levitt"
Silver has a bachelor's degree in economics from Chicago, but the saying "he might very well have taken a course..." is just bullshit. Sure, and he may have killed the universe's only unicorn while inventing a time machine. For Mann to excoriate Silver for his climate denialism and then follow that up with fallacious reasoning is delicious.
Second, Mann seems to assert that he knows for a fact that Silver took a class with Milton Friedman. Considering that Silver graduated in 2000 and Friedman retired from the University of Chicago in 1977...possible but unlikely. I wouldn't be surprised if Friedman continued to teach occasional courses at Chicago after his retirement (though he did move to California afterward), I'd be very surprised if he was teaching undergraduate courses.
Or maybe Mann did this intentionally...debunk SIlver and the helpfully provide an example of poor reasoning for someone else's column.