Both your stone and FW's look like natural cupmarks to me, though it's always difficult to tell from a piccy. Natural CM's tend to be smoother in the actual cupmark than man made ones and the edges of the CM are usually sharper and more defined with the cups being a lot deeper and often all the way through the stone.
Saying that though, natural cupmarks, I believe, would have caught the imagination of megalith builders and this has filtered down through folklore in terms of 'hag stones'- stones with natural holes through them that are believed to ward off evil spirits. I like em and have collected quite a few over the years.
I found a site last year which has both natural and what looks like man-made CM's on the same stone;
http://www.themodernantiquarian.com/site/6457
I re-visited last week with the digi cam and will post some better pics soon.