My current dog does too. He pays no attention to the TV unless there is a dog. He seems to notice the dog, even if the dog is quiet. He really gets excited if the dog barks, and he runs over to look behind the set to see if he can find the animal.
This morning he became very interested because there were howling wolves on a commercial. This particular dog is totally quiet himself -- never barks, howls, or whines (although he can). But he lifts his head right up as if he understands the language when a dog or a wolf is vocalizing on TV.
Mine runs up to the screen and barks at them, it's really funny. He even barks at the chia pet commericals and the cat commercial where they clink the side of a glass. Once he hears those clues he'll run to the tv to bark at the cat or the chia pet