A hippopotamos is not a (mythical, hypothetical or real) hybrid or chimera of a horse and something else. So that makes it a false analogy. It is a real, well known animal that lives in water, and mentioning it would not make people think of a horse.
The griffon piece is not so called for being the compound of a lion and an eagle. Likewise, the hippogriff piece is not so called for being the compound of a horse (knight) and an eagle. Each piece name is meant to make sense only in terms of the general chimeric nature of each mythical beast.
The griffon piece is not so called for being the compound of a lion and an eagle. Likewise, the hippogriff piece is not so called for being the compound of a horse (knight) and an eagle. Each piece name is meant to make sense only in terms of the general chimeric nature of each mythical beast.