Various sources suggest it's a literal joke, e.g. https://en.wiktionary.org/wiki/hippopotomonstrosesquipedaliophobia https://en.wiktionary.org/wiki/hippopotomon

Various sources suggest it's a literal joke, e.g. https://en.wiktionary.org/wiki/hippopotomonstrosesquipedaliophobia https://en.wiktionary.org/wiki/hippopotomonstrosesquipedalio...