Do you mean that he heard the terms "hookah" or "nargile" or "water pipe" and he didn't know what kind of object was described by the terms?By the way, Deborah, that American guy we met in Cyprus didn't know what a water pipe (hookah) is.
Or do you mean that he saw a hookah and thought it was a marijuana bong, rather than a pipe that's generally used for tobacco?
Or do you mean that he saw a hookah and thought it was a vase for flowers (i.e., he had no idea that it was used for smoking something or other)?
These are three very different levels of ignorance!