Why not elephant? After all, he is an elephant, isn't he? Much to everyone's surprise, Hippo actually proved them wrong.
"Well why would I be an elephant? I have a long nose, and no elephants have that. Why, then I would be... Well then I would have serious problems! Secondly, I have big ears. Thirdly, I can make a "BRRRRR" noise, fourthly, (goodness, this could go on for hours) I can store water in my trunk. Fively, I can spray that water out again!"
After much discussion, everyone agreed that Hippo had hippos and elephants all mixed up.
"Lastly," Hippo finished, "My name is Hippo." And that settled it.