The animators/modelers probably needed a bunch of knight weapons for this movie, and Nizzi made a ship load of them, so why ask a concept artist to make new knight weapons when there's a bunch of perfectly good ones already just waiting to be modeled? Or they were already modeled for Age of Extinction, but were never used. Either way, it's just a generic weapon, its owner probably doesn't matter.
Wasn't this black knight guy in AOE as a statue? I may be mistaken but sure he was one of the statues of the knights