Yes, I was there with them when that picture was taken. I recall Chris Burgess saying something like 'is that cup-and-ring?' and me looking at the stone and saying it's just erosion. Typically the stone is recorded incorrectly and the placename is Thornhope, rather than Low Thornhope.
There's still a lot to see at Thornhope - a huge amount of large stones but, sadly, they are lost in tall rushes and difficult to assemble conceptually. There are four or five stone rows recorded on the S.M.R. here and more visits, more images, would be welcome. Clearly there is more Rock Art to be found here.
I've dileted all the sites on here that are close to my basecamp - just for peace and quiet's sake.