Just look at the flaperon largest picture! I've experienced first hand barnacles on boat hulls too and they can grow everywhere indeed. But first, this is no standard boat hull materiel and certainly not at anchor. Plus the citation is a little out of context: not saying that they can't do it, but the number of barnacles on the Reunion flaperon's flat surfaces are quite limited with regards to angular sections and corners. Large flat patches are almost free of them and there are very few attached to the shattered ragged edge. All the newly parts found feature flat surfaces and ragged edges... And that may simply explain this.