Hi Sem,
Any idea what the local rock type is? It looks like it may be sandstone, or tuff. The different colouration suggests to me that these stones are less weathered than the surrounding rocks, whose colour will be the result of weathering and growth of lichens etc. As such, it seems unlikely that your stone is in it's original location, and may have been exposed (either turned over, or moved) relatively recently.
The holes are interesting. Any signs of toolmarks, or other markings within/around them? There are natural processes that can cause similar cavities, dependent on what the local rock is.
As seductive as the idea of undiscovered cup marks is, I think you should eliminate any other possible derivation first.
Look forward to whatever else you can reveal about this.
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