I don't really understand, seems like there is a very easy answer. In the case of belief I would've thought that's obvious. I can be afraid of zombies without believing zombies exist.

I don't think anyone denies the existence of the concept of god. I'm an atheist, but of course the concept of god exists. People believe in it, it can and has been talked about.

Seems like you're equating the concept of god (i.e. people's beliefs), with the actual entity of God (i.e. the man in the sky that created everything).