In my firt accounting class, the professor clearly stated there is no such thing as a non-profit. And since I work in an "institution of higher learning" dealing mostly with non-profits, I can clearly state the most popular, chronically over-subscribed course is Grant Writing.
Your professor didn't know what he was talking about. Ask the IRS, they have thousands enrolled as non profit organizations. It is just that your professor has his own definition of non profit which does not coincide with that of the IRS. That was a good one about Grant Writing.