I'm no expert, but you could have a million dollars in the bank and have a low credit score. Zero doesn't right to me, however.
Your credit score is based on a lot of things, one of which is having credit accounts and paying on them regularly; that's not tied to income. If you have a history of credit lines where you pay regularly, you're a lower risk and get a better rate. If you don't have the history, the risk is high (in the eyes of the crediter) since they have nothing to go on.