hot takes are already incoming, so just as a reminder: Sayings like this have assumptions that are necessary to be aware of before nitpicking details.

The saying is just saying that smart people are open minded to new ideas and information and indoctrinated people are taught to be close minded. It doesn't mean every new piece of information is immediately believed by the smart person or that smart people are immune to confirmation bias, just that they are generally open to new information supported by evidence and indoctrination teaches people to reject new information whether it is supported by evidence or not.

It is a generalization about a primary difference, not a hard and fast rule.