An ancient coin dating back to the tenth century BCE – roughly the time of the reign of King David – was recently discovered by a 10 year old volunteer from Russia who had been participating in the Temple Mount Sifting Project in Jerusalem.No, this was not a coin. Coins were not invented until some centuries after the time of this artifact. It is a seal — a stone object carved with an image (not writing in this case, alas) which is pressed into clay (or later wax). The clay impression is called a "bulla" (plural "bullae) and was used to seal documents shut. You can read about the story here.
This doesn't seem complicated to me, but this is the second time I've seen this sort of confusion recently. Back in June someone was confusing a Canaanite-era Egyptian scarab seal with a coin. Story here.