But seriously now : Even if it WAS an "ancient coin", this wouldn't be the first time that ancient coins have shown up in the oddest places. And as odd as it may sound, it DOESN'T mean it was an "ancient loss".
Because old coins (yes, even ancient ones) have circulated in collector circles since time immortal. And it's entirely possible (though rare) that they could be lost in modern times. FOR EXAMPLE :
1) In my neighborhood as an 8th grader with my first metal detector, I found an 1870s coin on the curb-strips in my neighborhood. EVEN THOUGH my neighborhood wasn't built till the late 1950s. How did I know it was a modern loss ? EASY: It was still in the bezzle. Doh !
2) As a kid, a family friend gave me a Roman coin, that he had brought back after a tourist visit (years earlier, in the late 1960s) as a tourist to the Holy Land. Apparently you could buy ancient coins from roadside tourist vendor stands, even then, at $1 each, blah blah. So .... what's to have stopped me, as a kid back in the USA, from having gone out and lost that coin here in modern USA ?
3) Returning veterans of WWI and WWII were known to have brought back souvenirs , which included coins. Yes even vintage coins, from the countries they visited. And "old coin collecting" is not a new human-instinct-phenomenon. Thus yes, they sometimes returned with vintage coins from all around Europe and the middle-east.
Is it odd that some of them could have ended up in some odd-ball sand-box or park or whatever ? Sure. But odd stuff happens. I knew a guy who found a shallow seated quarter from the dry sand of a tourist beach, while plying for modern change and jewelry. How did he know it was a modern loss (versus a loss from the seated era ) ? Easy : It was still in the plastic sleeve, with the price tag on it, from a nearby coin/stamp store. Doh !