Isn't Matchu a...um...Matchu? How well he know that Amber will be interested in someone who's not human?
Okay, for real, here's a better answer. In this universe "Chus" are more of a race than a species. There's gonna be a lot of freaks running around, you see. So Matchu and Amber is more of an interracial romance than an interspecies one.
Never stopped Roger Rabbit, did it?
I'd like to know why the chicken crossed the road, too.