On the contrary, I would argue that our default belief state is one full of scary monsters trying to kills us and whirling lights flying around overhead and oh no what this loud noise and why am I wet

There is no mention of God in that state; therefore it is atheism. Any person who does not believe in God is an atheist. Anyone who has never thought about whether there is a god, or doesn't have the concept of god, is therefore an atheist.