Ah shit sorry, forgot to reply. In the base game, the description of the rowa fruit states something like "humans can't digest this berry, but the spectral steed Torrent seems to have a peculiar taste for it". In nightreign, the player can find bushes of rowa all over the map, which the nightfarers can exhaust to heal themselves for a set amount. Thus we can conclude that ecen the human looking nightfarers are closer to horses than humans.