Narrow-minded means that a person subscribes to a narrow world view and is not open to new things. Perhaps they believe only in things that they have experienced for themselves.
Rush Limbaugh is an example of a narrow-minded person. His rant about classical studies, for example.
“Tell me, any of you at random listening all across the fruited plain, what the hell is Classical Studies? What classics are studied? Or, is it learning how to study in a classical way? Or is it learning how to study in a classy as opposed to unclassy way? And what about unClassical Studies? Why does nobody care about the unclassics? What are the classics? And how are the classics studied? Oh, cause you’re gonna become an expert in Dickens? You’re assuming it’s literature. See, you’re assuming we’re talking classical literature here. What if it’s classical women’s studies? What if it’s classical feminism? Who the hell knows what it is? One thing I do know is that she, the brain-dead student, doesn’t know what it is, after she’s got a major in it. Because all she knows to do with it is go down to Occupy Wall Street and complain and write a note for the cameras.” Source
A person who was not narrow-minded, if he did not know what classical studies was defined as would have looked it up before ranting about it.