No, it really isn't. A number of my close family are agnostic theists. They genuinely believe that God exists, and they believe in God. They also accept that they do not know God but, for whatever reason, they do actually believe. They don't believe scripture is divine revelation but believe that much of it makes sense, including, to them, the notion of God. If you asked them whether or not they believe in God then they would say that they do, so they are theist (or would recognise that as a label applicable to them). If you asked them whether they have knowledge of God they would say that they don't, only that it feels right to believe, that they are comfortable with it, that it makes sense to them, etc. That makes them agnostic. Put the two together and you don't suddenly get an agnostic atheist. Without other theists around, these agnostic theists are still theists, and still believe in God.