He's right. Forest Elephants(Aka "Bush" Elephants) are/were a separate species to the African Plains Elephants. And, as far as I know, those Bush Elephants were very small and couldn't support any kind of Metal armor.

In fact, doesn't a Roman historian mention how the Numidians would paint the outsides of their Howdahs?(Basket Tower thing the Archers/Peltasts ride in) They would paint them so that they looked like they were made of brick to fool their enemies into thinking their Elephants were stronger than they looked. I think it was Polybius who mentioned it but knowing him it could be entirely made up.(Would've been pretty smart of the Numidians if they could've done it though. )