I don't know enough about FR vampire lore to know, but I thought his line about the wine being sour, which you can taste and have described as rich, was a result of vampires not being able to enjoy food. Is that a thing? from that view point I think his disposition at the party could stem from his feeling alienated from the mortal world, even when he's been lead to behave morally...but it's not really a lot to go on.
