What it says -- you shouldn't be getting paid to work on other projects. This is mostly to keep your head clear and focused. I and a lot of my friends are so burnt out after a day at work that side projects basically never happen. I want to remove this burn-out for someone.

Okay, that makes sense :)

I stand by my recommendation. Few people do more for open source than Sven. (Bonus: I don't think he's usually employed.)