You do find he is a Shadar-Kai by killing him, and a rogue one at that. On his corpse is a letter from another Shadar-Kai scolding him for going AWOL despite the commands from the queen to return.
It turns out not even the Shadar-Kai are safe from Shar's shadow curse. It corrupted one of their agents into strangling their raven familiar, and the shadow queen killed that agent as an example and called all Shadar-Kai to leave the Shadow Lands and return to Shadowfell.
