Yeah, it was easy to tell that he was a rat. Rats are often used for tv and called mice due to people still being afraid of them. Not to say that mice can't be trained as we saw in the movie The Green Mile with Mr. Jingles and the mouse in Mousehunt.
Also in the remake of Tales of the Riverbank which was renamed Once Upon A Hamster, they used another rat named Martha, which they also labeled as a mouse. http://www.youtube.com/watch?v=B-CtMWsMGGo
<-- here you can see that in the first series from 1959 they actually called the rat Roddy the Water rat, and in the show. They should have stuck with that!