It's not a very narrow interpretation of work - it's the one that matters in this context, and the one that matters day-to-day. Sure, you could define work as anything one did that had results you find interesting, but the narrower definition that's important here is things you do because you have to, because you're obliged to do them by others or by circumstances, vs. things you do for fun - because you want to, and which you control. A job vs. a hobby is a good approximation. It's not uncommon to see people being much more effective at their hobbies than at their jobs, even when both of them are in the same domain. It's also not uncommon to see a hobby to be more worthwhile than one's work.