I disagree with this claim. I know what you are referring to and I have seen the rock art you speak about (and I agree that there are 'some' similarities everywhere) but I also think you haven't seen galician rock art itself. Many also suggest a random origin for rock art in Galicia but the fact that it was unique in Iberia and EXACTLY the same as British rock art (NOT Irish) make it a strong contender for some sort of cultural trade links.