At 21, your title is just meaningless words to sucker you into working longer hours. The unfortunate thing for the author is that he thinks he's learned something about being a good PM, but he's really just learned how to be a good junior; "listen to the experts and leave your ego at the door".

To me a product manager needs to have vision and empathy. Vision, to know where the product needs to be in 5 years. And empathy to be able to truly understand your users needs. From the article, it doesn't sound like the author learned these things.