That's an overstatement. You can build impressive MVP and tech demos in a short amount of time, yes. But that requires that the author has already been thinking about the types of problems that come up in this domain for a long long time. Rest assured that Git certainly hasn't been created in a weekend.
Also, you can't create a product in this short amount of time. (There are some websites that do almost nothing at all, and that are very profitable, but those aren't engineering problems). Think how long git has been maintained, polished, and extended since its inception. And still people complain.
Software is a learning process, otherwise people wouldn't be so obsessed about it. And learning takes time. No matter which way you're approaching it.
I agree, saying Git was created in a weekend is like saying olympic gold medalist in 100m dash won competition in 10 seconds. Linus was working with DVCS software already and was annoyed with it so he had an idea on how to do it, he did not came up with it on Saturday like it never existed and coded it on Sunday.
Other part about Facebook - well if you take first version that was just well photos + some description and disregard all stuff that was refined next years where it started to be real product instead of novelty page for Harvard students.
In a company I work for we built first version of application in 1-2 years to catch up with what other companies already had and what customers expected. We could do really simplistic version in a weekend but no one would pay for it.
Also, you can't create a product in this short amount of time. (There are some websites that do almost nothing at all, and that are very profitable, but those aren't engineering problems). Think how long git has been maintained, polished, and extended since its inception. And still people complain.
Software is a learning process, otherwise people wouldn't be so obsessed about it. And learning takes time. No matter which way you're approaching it.