It doesn't mean it's totally irrelevant, so much as the fact giving us a confirmation those rocks are from SG may not give us any huge clue about the relevance of that detail. If it's tied to a prophecy, the revelation in itself would be a huge spoiler. It for instance it merely extends the DO's powers in another location beside SG, or increased Shaidar Haran's powers to act there/in Caemlyn, it's not a spoiler since we currently don't know of any property anything brought from SG might have and everything is thus purely speculative. As I said above, that those black rocks have been brought from SG has long been suspected.