Hmm, in hindsight there were a few hints about this all since the introduction of Faceless (e.g. the dog taking a liking to him). Still, this does seem a bit unexpected in some way, maybe beacuse all those hints were really details, spread far apart, and rarely shown as being mysteries.
Let’s see how this plays out, it is possible there comes a more thorough explanation after it that also was skipped in the anime.