An organisation is a legal entity, its books show a profit or not. When someone is making paid for doing a job, it does not equate that a profit is being made. It is not even true that a board member could not be paid a salary because otherwise the legal entity is an for profit organisation..
The argument does not make sense.
Exactly. Non-profit means there aren't shareholders getting paid dividends. That is, you can't get given money by virtue of owning part of the organisation. You can get given money in exchange for services rendered.
That said, I don't think WMF paying its board members would have any considerable advantage.