Going to throw out a guess and say it's because selling you an item after you called it a bong is admitting that it's indeed a bong.
My second question is that if bongs and water pipes are the same thing, why does the law distinguish their purpose by their name? It seems like given "I want to buy a water pipe for smoking the marijuana" and "I want a bong to smoke tobacco", the second should be legal to request, not both.
if you intend to use that power tool or crowbar to break into a house it’s “possession of burgular tools” and a felony, if you’re a contractor there to install some drywall it’s not.