[Gunner]

Tomato, tomahto.

I spent 15 years in electronics design and a few years here and there in things like theatrical lighting, independent power generation and the like. The terms are completely interchangeable except that no one in electronics (since about 1945) calls them rheostats. Since he was being directed to Radio Shack to find a part, pointing out that the ignorant nebbish behind the counter isn't going have a freaking clue what a "rheostat" is was intended to be helpful.

Nor is the guy at the wrecking yard likely to know what a pot is. Theatrical crew, flip a coin; the older ones and ones who work on really large gear call them rheostats, the newer guys and ones who work with small theater gear call them pots.