They are still a theist. Theism is the belief in a ***/gods and so someone who has that belief is a theist. It is also why someone without a belief in a deity, like myself, are called atheists (which is 'theist' and preffix 'a-' meaning not/without - that is, a person without a belief in a ***/gods). An agnostic, in case you were wondering, is someone who believes that *** may or may not exist.