I think the article is saying that, should you read something interesting, pursuing that interest will provide meaningful insights. The author is saying that "sources" aren't as relevant as the history of interesting ideas. They are not saying read all sources. Just read a lot about the things that interest you.

I find this strategy works very well for so many topics, specifically politics, economics, history, and more. Read 5 books on contemporary economics and you will be infinitely more informed than if you watch economics or market segments on news stations for 5 years. What you'll learn by reading those books is more than just some dry economic tautologies, you'll see the history of economic theory. So and so theorized economics like this, then they were disproven, then someone started talking about behavioral economics, etc etc. That seems to be much more useful than any alternative I know of.