In my own personal experience -- which I presented immediately after the sentence you quoted -- I didn't originally understand how to visualize, and then later discovered more about how to actually visualize.

So clearly it's not like the case where a person is born without a sense of smell, because in that case nobody's going to present an "at first I didn't know how to smell, but now I do" story.

I'm not saying that all people who experience aphantasia are "just doing it wrong." But I can assert that in at least some cases it is a skill issue, because one of those cases was my own case.