Not sure if this is a bug. Ching Shih's Red Dragon and Sadie's Porkchop are labelled Legendary outfits. All other Legendary outfits carry buffs: those 2 do not. Seem out of place. But perhaps it's just a rarer outfit that makes them Legendary.
Those two outfits were original legendary before we had voodoo and Viking outfits. They cost gems on the trade ship and are considered legendary even though they have no buffs.