Why can't it be a Riekling? It's clearly a descendent of the elves.
Probably could be. Anything's possible.
For all those saying undead, I want to point out the quote I posted earlier from Fall of the Snow Prince:
"His spear and armor bore the radiant and terrible glow of unknown magicka, and so adorned this unknown rider
seemed more wight than warrior."
This is total conspiracy theorizing now, but that makes it sound like at least the Snow Prince, if not Falmer in general, had a sort of pale undead look to them.