It's unclear what the coating is, but it's called "Ceramica" and it's under the Cuisinart hard-anodized product line, so it's probably just a smooth hard anodization process. My guess is that either it's scratched (unlikely, as aluminum oxide is 9 on the Mohs scale) or that something stuck to it in one spot and it built up.

I'd say scrub the hell out of it with some salt and baking soda with a green scrubbing pad and see if it removes all the stuff you can't see.