No, Daus isn't human. He's a changeling. Yes, he said that-- It was a lie. He does that. No, no, there's no such thing as an Honestwizard. He's an illusionist. That wasn't even one of his good lies, it was one of his wierd joke lies. He's got a strange sense of humor.
It's pretty easy for a good liar to impersonate people, yes. That was one of his favorite games growing up; for a few years, getting people angry at each other was fairly easy. His family's not stupid, so of course they caught on eventually. He'd surely have grown out of that game by now regardless, right?
I suppose he's got an interest in his father's craft. That orb he carries? He made it himself. There's some gadgetry inside that moves his magic about, just like an enchanted orb focus would. Not an ounce of actual magic in it, either. He can do some neat tricks with that thing.

Yes, he does look different. 'S another thing he does; he tends to come up with different looks depending on the situation, the weather, his mood, and on. He usually looks human, though, now that I think about it. Likes the way they look maybe? Can't count on it o' course; he'll only look the same as long as it pleases him and not a moment more. It's important that things look the way he wants, right? The nose is too big or there's too much red in the scales or...
Look, don't try to remember what he might look like. Just keep track of him. And hope he's not messing with you.