I think the point is that if you're trying to convince someone to pay you to write code for them and you have no prior experience with professional programming, a solid way to convince them that you're hireable is contributing significant amounts of code to an open source project. This demonstrates that 1) you know how to write code, 2) that you can work with others and 3) that you're comfortable working with a complicated codebase (depending on the project).
I'm not certain that its the most effective way to achieve this objective, but I can't think of a better alternative. Suggestions are welcome.
Related to: Optimal Employment, Best career models for doing research?, (Virtual) Employment Open Thread
In Optimal Employment Louie discussed some biases that lead people away from optimal employment, and gave working in Australia as an option for such employment. What are some other options?
Your optimal employment will depend on how much you care about a variety of things (free time, money, etc.) so when discussing options it might be helpful to say what you're trying to optimize for.
In addition to proposing options we could list resources that might be helpful for generating or implementing options.