Well:
The issue of being theist or atheist is somewhat obviously not about knowing if a god is there (cause, surprise, you cannot). It is about thinking, and the forking path of either thinking you know a god exists/doesn't exist, or thinking it is likely a god exists/doesn't exist. Knowing whether a god exists is not part of the equation in any logical examination of a belief.
Agnostic merely means that you think you cannot know (about something, and god in this context). It never is about thinking there is ground enough that you can form a speculation about what is more likely to be the case.