I think a heckhound is a type of wolf. Not a dog. And the cats don't look like the dogs because they are a different type of animal because they are cats NOT dogs. Who doesn't know that a cat isn't a dog?? Oh and the subject isn't the right title for your question because you're also asking about other animals not just dogs.
Whoa there flamo. He said cats and MB cats. Also the title doesn't have to be define the exclusive content 100%, relax, take a deep breath and chill.
As far as the OP, I would imagine that the fire cat and heck hound, in this weird warped reality that is W101, they are mythical magical beings with special powers and the dogs and cats of MB are the people of their realm. Good question though.