Every??
Many buddhists would disagree with you.
Theism is the belief in the theistic notion of God - so is certainly a component of theistic religions.
But you can be a theist without being religious - e.g. believe in the theistic notion of God without adhering to any practices proscribed by one of the many theistic religions.
And you can be religious without being a theist - e.g. certain Buddhists, I understand. Pagan also, I'd have thought.
One could argue that Buddhism isn't a religion.
If you believe in reincarnation then you have a religious belief system. Not to mention the other formalities and commonalities. If anything thrn scientology is less of a religion than Buddhism is. Anything supernatural belief is religious in nature.
Someone who belies in aliens is not religious because alien (from another planet) is not a supernatural belief.