Well, I meant it in a relative sense. Introverts take in more information per perception, which is why they're easily overwhelmed by experience and must retreat to solitude to process all the data. Extroverts take in less information so they must seek out more experience to reach the same level of understanding as an introvert. This isn't to say that extroverts are less intelligent or knowledgeable than introverts, but the former must work harder to acquire their knowledge, by going out in the world and acquiring more data. The "shallowness" has to do with how much information is processed per experience.