Indian Rhino and Hippo is nowhere near as bad of a mistake as some I've heard. Think about it, both are heavy-bodied, similar colored mammals with a similar enough look to them, and Indian Rhinos do like to swim, something a lot of people don't associate Rhinos with. Furthermore, Indian Rhinos don't exactly look perfectly like the African Rhinos people are used to seeing. And anyways, I've heard people say much more bizarre mos-identifications, like calling a sulcata tortoise a kitty, calling an emu a big duck, calling a red panda a lemur, calling a sloth bear an anteater, calling a leopard a tiger, calling kangaroos dogs, calling a lemur a fox, and many more, equally bizarre misidentifications. Your rhino/hippo example at least has an understandable line of reasoning as to how they came to their conclusion.