I'd go quarrying there FW.

If you call those cupmarks (and they're on the deep side for cups) then they are canoe-shaped cupmarks. Even allowing for a couple of hundred years erosion they are not a splintered, jagged, and just generally nasty, as you'd expect 'quarrymen's marks' to be. I know you think the Megalithic Inch is the invention of fairies - despite its continued use in China, Asia and wherever acupuncture is practised - but it is a simple way of pseudo-verifying these things.

I'm tempted to post an image of what quarrymen's marks really look like. I've posted it before. And, with the canoe-shaped cupmarks there's always the open question of 'if they went to all that trouble to mark the stone why did they then abandon it' ?