IMO, the entire cutting out a headset theory makes no sense, nor does comparing it to seatpost
Seatposts have plenty of surface area for potential binding, compared to the 10-15mm depth of a head cup.
Also sestposts are pulled from the blind side, vs. headsets which are easily pushed from the bottom.
Lastly, this is an aluminum frame, so galvanic corrosion isn't likely, nor does any evidence of it show in the photo.
Of course ANYTHING is possible, and we'll never know.
So why waste so much time on it.
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A last thought offered for whatever it may be worth.
In my 50 years working with all sorts of mechanics, in various contexts, I've found that those most boastful of their skills and credentials are usually the ones on the shakiest ground.