There are many solitary corals that live in the sand in nature.Cynarina sp.,Trachyphyllia geoffroyi(open brain),Catalaphyllia jardenia(Elegance) are just a few.A good way to tell if it came from the sand in the wild is to turn it over and look at the bottom of its skelton.If its conical shaped,then its a sand dwelling coral.
BTW,don't bother buying an Elegance coral,they are overcollected as is and they have a dismal survival record.