Is the Atheism/Theism belief/disbelief a false dichotomy? are there other options?

[Pyrrho]

Are you then saying that a person believes or disbelieves, regardless of whether they are certain about it or not?...

I am saying that one either has a belief in a god or one does not have such a belief.  ("Disbelieve" is problematic in this context, as it sometimes means "Be unable to believe" which is something a little different from merely not believing.)  Now, the question of how one determines whether one has a belief or not is a separate issue, but that is unimportant to the point.  This is why I earlier introduced the idea of me having undetected cancer.  I KNOW, ABSOLUTELY, the following:

Either I have undetected cancer or I do not have undetected cancer.

Now, I do not know that I have undetected cancer.  And I do not know that I do not have undetected cancer.  But I know absolutely that either I have it or I do not have it.  That is because that covers all possibilities.  It is a tautology, true by virtue of the meanings of all of the terms (mostly due to the logical concepts of negation and disjunction).

The same idea applies to anything else of the form:

p or not p

where "p" is any meaningful statement, and "p" has precisely the same meaning in both instances.  Thus, it applies to the idea of being a theist.  One either is a theist, or one is not a theist.  One may not be able to make a determination about someone, which they are (a theist or not a theist), but we can be certain that one or the other does apply, due to the fact that "not a theist" covers absolutely everything other than a theist.

So, with a person who does not know if they have a belief in a god, they will not know which applies to them, theist or not a theist.  (Which makes it just like my undetected cancer example above.)  But they can still be certain that they are either a theist or not a theist.