Is that a joke, or does circumcision or its absence actually have an effect on the classifier? Or do you refer to some other characteristic? Offhand I can't really think of a more marked difference between American and non-American penises than the relatively high US circumcision rate, but I'm not so much a subject matter expert as just an interested amateur, and perhaps I overlook something here.
(If anything, I'd expect the classifier to more reliably call "not hot dog" on a penis that's circumcised, since hot dogs rarely are.)