I'd agree, someone with some knowledge of rock art "carved" it recently.
Vandalism may be too strong a word, maybe it should be called modern art, Though i use the word "art" extremely loosely.
Megadread, I'd say if modern, it's a little more than 'some' knowledge of rock art.... well certainly from the bottom motif anyway. There can't be that many modern Rock Bothering saddo's (meant lovingly) who'd think to truncate an outer ring and incorporate a smaller multi ring in a Chatton styleee...