Nope. A customer is someone who gives something back for the service, period. If you make charity, the people you help are not customers. Paying or not paying is what makes the difference between being a customer or not. Firstly, because you will usually try to conform a customer better, because what you get is not gratification only for what you did, but a pay. If you do it just for the gratification, you can quit doing it when it stops being rewarding, and you don't need to listen anyone else. And again, nobody says opinions should be discarded outright.
If you're working as a volunteer programmer, you're customers are the people using your software. Deal with it.