Semi-key date surface find!

A few weeks back i was at the old hotel/pavilion site and was searching right by the lake. The iron was overwhelming and it was about 105°, so i was about to admit defeat and leave. Then i saw a small green disc on the ground. I wish i woulda photographed it so i could prove this now, but I had no idea what it was. After an olive oil bath, i found it to be a 1910 wheat. I was very impressed, and after ogling it a fair amount, threw it with the rest of my wheats. A few weeks later I’m looking at it under a loupe with a built in light, and i see the “S” mintmark! In normal condition these go for 20-50$, and mine is in such bad condition it’s probably not even a 5$ coin, but the fact that such an old semi key was on the surface amazes me. Idk if you can see the mintmark in the picture.its a tiny smudge that i would have thought was a “D”, but no 1910 d’s were minted. Thanks for looking!