Afraid I'm with Lindy on this one.
It was an interesting post, and as Lindy says, she actually pointed out the most rational explanation.
The stone is likely a modern artistic endeavor, although I don't agree with the opinion that this kind of carving is beyond more "primitive" artisans.
Whether the "finder" actually found it, or was in on it, is not important.
The pattern was then copied by human circlemakers.