Too general, too vague ("derived" from the generally applicable lies about just anything, in any human profession, any hobby, any kind of activity). Typical example of an unsuccessful attempt to be amusing, fun, clever... Let's analyse the "lie" that the author of this bad joke regards as being the "very special" one, because "photographers tell it themselves" - to think so or say that with the better camera one will take better photos is an ABSOLUTE truth. Not an ATOM of a lie can be found in such a statement/conviction. Let's suppose that you used to shoot with a decent point'n'shoot camera. Now, you've upgraded to full frame Nikon, Leica, Canon...Hasselblad...The same objects, people etc. that you shot before are going to look MUCH better once you re-shoot them, under the same light conditions. Colors would be more accurate, level of details higher, there would be less noise, textures and "lines" would be sharper, with less artifacts... The difference would be obvious, right away, at the very first glance, especially if printed at max quality or viewed in it's full size on a professional, high resolution monitor. Period.
What the author (probably) meant (but wasn't able or wasn't willing to put it correctly) is that there are PEOPLE who think they are going to automatically BECOME (good) photographers once they get themselves a (good) camera. But this is something completely different.