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.
I didn't read the letter because I didn't fight or kill him. But if he is a traitor to the Raven Queen...then the only possibility for saving his soul is to kill him. Usually Shadar-Kai are immortal...if they are killed the Raven Queen resurrects them in the Shadowfell. But the soul of a traitor? To betray one's own god leads to one of the worst fates imaginable for the soul. Either way his only chance at salvation is for us to kill him ASAP and hope that the Raven Queen shows mercy and reclaims him before he does anything more to anger her.
This makes it far more important for Larian to allow the player characters to be followers of the Raven Queen...whether by being warlocks or clerics or even Paladins if that is what Larian fancy though I wouldn't really expect to see any Raven Queen paladins as paladins aren't really her jam in the existing dnd lore as far as I am aware.
