If that was found in the wet sand, then either :
a) it just fell out of the upper dry dunes at some point in the very recent past (storms of last season reaching up high?) . And then had JUST enough time in the wet, moving with the tides/sand, and cleaned by the salt water. JUST enough time to get a shiny appearance, but NOT enough time to develop salt corrosion. Or
b) could be a recent loss. Although not likely. Since wheaties haven't circulated for 30 or 40 yrs. now.
Ya never know with this hobby. Odd stuff shows up anywhere
Congratz on your oldest.