I am certainly onboard with something like that being the root cause for this coin. I've looked at it a couple times now and the one thing that keeps me from believing it is an error coin is the separation lines on the reverse. Usually there is at least somewhere you can see a crack extending a little bit under the unaffected area, but on this coin I really just don't see that. It's somewhat smooth, and that's troublesome and leads me to think it's
PMD. The detail softness is also pretty similar to an acid-dipped coin, although usually there is at least some pitting. The diameter isn't greatly shy, just 0.1mm, but in the
Coin World that's a lot so also leads one toward the
PMD answer. Still not sure, but for now things seem to be drifting toward damage.