I'd take the handles and knob off and run it through the SCO. That will even out the swirl polishing on the bottom.
Is that weird texture on the inside of the lid too? If so, I would bet it was in lye for a little while. Not too awfully long, but long enough to etch. It would cover all of it though. If not on the inside, I don't know. it is odd.
A little buff with 0000 after the oven would take care of it, in my mind anyway.
Tom
addendum: I had not fully comprehended your post at first. I assumed you had cleaned it already. If that is how you found it, I would think it is silver paint. A cruddy job, but paint. Hit it with a paint remover and see. Paint on aluminum is odd, but there are some odd folks around.