There are lots of ways to screw up a smooth polished surface, physically and chemically. What’s you hypothesis?
My first thought (and hope) is that yeah, in this case it just needs some more cleaning, and as I originally suggested I would do that with iso alcohol followed by mild detergent (thumbs up to Dawn, Save the Ducks!).
Here I will say my experience is similar to
@Stu's; for me there is often, even on glass, a film, or perceived residue left behind after an iso wash (or thorough wipe) and that seems to go away with the detergent wash and some amount of water rinse. I have wondered if this is more a factor of the 99% iso I have used for a few years now. Is it too strong?
If 'normal' cleaning is not effective, and based on the description we have,
I'll divide the possibilities into two classes. The first as I said, just seems less likely to me and that is that someone used an abrasive, something too "scratchy" whether it be emery paper, Comet, steel wool, whatever, to try mechanically eroding perceived buildup on the surface. Not a scientific hypothesis, just a matter of where I'm guessing likelihood lies.
The second classification I would broadly call solvent/detergent/cleaning agent type stuff, something used in an attempt to "wash" or "dissolve" the perceived buildup away. Anything from hot water to iso alcohol to PBW, etc, etc. on up to Simple Green, or a zillion other possibilities. Since I'm not a metallurgist, I don't know enough to make a list of the things that can damage anodized aluminum, but some googling has shown me there could potentially be a long list. (I read one article describing 15 types of aluminum corrosion, for example!) Great rabbit-hole fodder...
And the Google even led me back around to FC, to the conversation
@RustyOldNail pasted (above) from 2015, in a different grinder thread!
Without citing sources, 'cause it made me dizzy, I read in one place that anodized aluminum should not be subject to a ph outside the range of 4 to 9, over or under, a Goldilocks type thing. And another that told me PBW dissolved in water has a ph of 11.2, so I just don't know...
And I don't care to be a metallurgist, so I just load another bowl and vape on...
We've still got 2 months to postulate, speculate, ruminate and regurgitate, but there's a large amount of stuff we just don't have the information on, so I propose we load another bowl and vape on.