Preface that I felt I should add: This is not an attack on you.

I've seen this diagram before, and I find it very unhelpful. First of all: The top sentence in the two top fields says "Does not believe any god exists." - which is super ambiguous. It should have been "Believes that not god exists." or "Does not have a belief that any god exists." That people see such a diagram on the Web and say "Oh, now I know what these terms mean!" is part of the reason we have all this confusion in the first place. Then there's the question if all these 4 directions are scales or digital choices. And finally, what does the zero point between the two horizontal fields mean, and then what does the zero point between the two vertical fields mean, and what does it mean if both are a perfect zero? This diagram is the definition of confusing, and it aims to explain one of the most fundamental categories today's mankind deals with. It gives people the impression that they just learned something, but everybody walks away with a different interpretation. That's just like the Bible and such.

although I would add a split in the middle, as it is possible to be 0% confident in your belief but still be either an atheist or a theist.

And that's the key point with which I fervently disagree.

If I am perfectly undecided if God exists, then the strength of my belief that God exists is 0.00...(Infinitely many 0s.)%, and that means that I do not have a belief that God exists, meaning that I am not a theist, meaning that I am an a-theist. This is not a decision whether or not God exists: I am perfectly undecided. But that means that I have not the slightest "Yes, God." decision in me, which means that I am not a theist.

You see it differently. Could you break down why that is, or how you would phrase kinda what I just phrased, except supporting your view?

Again:

although I would add a split in the middle, as it is possible to be 0% confident in your belief but still be either an atheist or a theist.