I think pretty much what you said. If you write, you're a write. While I don't care for Stephanie Meyer and think her stuff is crap, I admit she's a writer. I think it's useless to claim that someone isn't a writer just because you dont' like them. However, I think you're a writer if you make a point to write outside of requirements. For example, writing a history paper for a class required for a major does not make you a writer, because you have to do it. Making a conscious effort to write an essay on history because you are genuinely interested in the topic and then submitting the essay to some kind of contest or keeping it for yourself or whatever you do with it makes you a writer.