In his middle-age he became multi-millionaire from nothing, so he definitely can talk about business and wealth creation. Although the book is just a summary of the philosophy of a particular person.
"Making money is not a thing you do – it’s a skill you learn", - he also said if you drop him on a random English-speaking country, he will recreate his wealth within 10 years, just because creating wealth is a skill. Hopefully, it is true, and later in the book Naval teaches as how to do so.
The point is that wealth creation is not just about hard work. Hard work, if you exchange your time on money as an employee, got you a proportionally bit much money. It is a linear relationship. If you want a logarithm relationship between your effort and outcome, you should do business.
“Wealth is having assets that earn while you sleep”, - easy to say, but hard to do. Naval gives us an algorithm.
“Fortunes require leverage. Business leverage comes from capital, people, and products with no marginal cost of replication (code and media)”, - the picture becomes more clear, right?
Let me paraphrase: use your unique skill, build a business around that skill, use leverage in order to boost your deal (technology, media, capital, and labor are boosters), and be an owner. Share in businesses (your own and portfolio investments) makes you rich, not exchanging your time on money as an employee.
I think we should remember: the book is just a point of view, a successful person though. It is not a silver bullet, but friendly advice and personal philosophy. We can apply this advice and build our own philosophy.
P.S. You can download the book from an official website.