I also thought it was just Hyuuga's remains. Perhaps they had boosted their stocks with the remains of other ships they had sunk as well, although they haven't seemed overly eager to salvage anything after the fights we have seen. That's almost a plot hole, unless using nanomaterials requires a permission from the original owner and thus robbing it would be impossible. Unless Admirality is involved, like Iona's case, and also Kongou's, I suppose, just proved.