Not to speak for the author...but, well, here it goes...

I read that point to specify that you don't have to pay them in money, rather there are other currencies that are out there that can be far greater than money; like stock options, connections, real life code examples, etc.

All of the points you mention about the pitfalls of "unpaid" persons can be seen with paid employees as well. It just seemed like he was saying that there are alternative currencies out there other than just money.