that's a pretty big deal right there. right next to it some flesh still lives in another cup to the right, might come back there too. I cannot tell from one polyp, but the stony lps coral 'siderastrea radians' is a common hitchhiker when choice quality live rock is used, from the ocean, and their empty skeletons are often found coated in coralline and fused to the side of the rock since ancient days when it was alive.
that appears to be a survivor. Its value ranges, if you were my neighbor and brought that over, id pay you $30 to let me dremel it out of the rock facing and keep it as a frag. it has value to me for its rarity. I think that is a naturally-survived SR coral/