Pelo menos de acordo com a wikia , você não precisa ter sangue élfico para poder usar o Black Elfstone, então o personagem que você menciona não precisa necessariamente ter:
Unique Properties
Unlike the blue Elfstones, the black Elfstone does not seem to need a sufficient amount of Elven blood to be used, nor does it need to be freely given. Despite Walker Boh's Elven blood being extremely thin, he uses the Elfstone with ease, with none of the problems Wil Ohmsford experienced with the stones. He is also able to use the Elfstone despite having forcibly taken it from Uhl Belk, unless one considers the fact that the Stone King allowed Walker to leave his dome without a struggle as a sign of consent.