massive spoilers below!
Well, it's suppoused to be dark because the Mithalas guy is dying, so you're talking to his spirit telepathically. Or rather his soul was talking to you telepathically, not the other way around. This is kind of opinion, but I guess he was a good bieng in his soul, despite his corrupted body. Also, he must have had a more human form once, instead of the dragon-like form that you fought.