Intriguing hunch. Wonderful new arrival in a place you know very well. You would notice a new arrival like that! Local-ish new arrival? Or somewhere more distant (it looks a little similar in style to the "top" of http://www.themodernantiquarian.com/img_fullsize/126167.jpg ) . Very interesting design and the cup/rings are "stylish". Cheers!
The stone you linked to is about 10 metres from the new one and both are adjacent to a new hydro track . There are now 23 marked rocks in the area, none of the other 22 have the same level of preservation of markings including those under moss/turf , another reason for leading me to believe the new one has been been dug up and is not in situ .