I always wanted to know myself.. I once saw a video where they used a concentrated water stream to make precision cuts into wood, metals and also coins! very clean cuts
I supposed it could have been done very carefully with a dremel tool but it looks too clean for that. Cool piece though. I like it, irrespective of value.
A couple in my sanctuary They were high pressured punched. Rev to obv on mine. Both were taped to something and have residue