This is not advice for survivalists. It is advice for people who want to lead an interesting life. In his case he wanted the freedom to travel and work on free software back in the 80s. His skills as a waiter provided a safety net that gave him the freedom to do that.

Growing your own crops would be an absurdly horrible strategy. Imagine that you're in a strange city and your wallet was just stolen. You have just a few days of reserve cash. Would you at this point prefer the fallback plan of, "Plant these seeds, wait for them to grow" or "Get a job as a waiter, eat immediately"?