That my sir, is very interesting, unfortunately not a mint error but that may be worth a dollar or two to a exonumia collector!
You coin was stamped after it left the mint. Anyone can do anything to any coin at any time. that in itself does not make it an error. You have to find an "error" that is done during the minting process. Not by someone, anyone, afterwards. read this as a "starter" for understanding. then remember that 99%+ of things you come across are considered damage and not mint errors ==> https://en.wikipedia.org/wiki/Mint-made_errors
That is a "Pop out" Repoussé coin. I have a small collection of "pop out" coins. I have your coin too. novelty coins. Yes people collect these too. I would say yours is in the value range of $30-50. Here is a link to a thread here on CoinTalk about pop out Repousse coins... of which shows my collection of them... link: https://www.cointalk.com/threads/repousee-coins-aka-push-outs-or-pop-outs.225062/
As stated. Mint Errors occur during the minting process. Deliberate damage are not errors. Let me advise you nicely.. If you find a coin that looks strange and different you should first ask If it is actually a Mint Error or not.. If it is then worry about value.
