I think your coin may have been part of a school sciece experiment, having to do with electrolysis that redused the weight. A soak in mild acids can also produce a coin that look similar to your's.
That's an Acid Dipped Nickel. Corrosion affected it. Acid Shrunk Coins https://share.google/yfLpr195hTJmCsgBm Not a mint error of any kind unfortunately.
To be on a wrong planchet, it has to be smaller than a nickel. If it was a 1964 penny your coin would be 95% copper. If it was a 1964 dime, your coin would be 90% silver. The mint did make foreign coins from time to time and that is possible, you would have to look up what coins they produced for other countries in 1964. (It's not going to be a foreign planchet in this case.) The acid thing is very common as you can see the rim and the rim lettering is still there, if it were a dime or cent planchet the rim and lettering would be affected and partially missing. You can also see how thin the coin is which is the result from acid. Because of the damage, you can't even put this coin in a self serve machine as it will be rejected.
