In media, you're probably right. However, his point remains. Dolphins, Humans, Dragons are all "animals". Dolphins have the 2nd most powerful brain on the planet, form stable societies, social groups and have a language of their own.
SO, if Dolphin + Human = Beastaility, then Dragon + Human = Beastaility. Neither have the matching organs to make it possible, but at least Dolphins are mammals.