I believe it's not Vivienne who told him he sounds like a Pride demon, but the other way around:
Solas: Enchanter. Any Pride Demon you met would just walk away, shaking its head and laughing uncontrollably.
Vivienne: Oh, darling, more than one already has.
But, the fact that he is the only one not depicted as an elf is interesting, I agree.
Solas: Tell me, Enchanter, do you even bother to explore the Fade in your dreams?
Vivienne: I prefer to explore the world I actually live in.
Solas: A pity. You could be much more if you went outside your narrow preconceptions.
Vivienne: Ah... The temptation to leave the path... You sound like a pride demon.
The rest is as you stated, but I remember thinking it unnerving the first time I heard that conversation. Maybe it's just the effect of the Harrowing in he Mage Origin. That intro left me mistrustful of anyone in Thedas ever since.
