My whole point is bad writing took casting decisions in the 70's and conflated that into "see how evil the empire is and how good the rebels are?
The detention officer in that case would of known what a Wookiee was, and the look on his face and his tone of voice clearly was intended to carry a sense of disdain for the Wookiee.
Also the xenophobia of the Empire was something that was part of the Empire from the start, it wasn't just something added in with the EU to cover a plot hole or something.