Everyone know what "clip" means colloquially. The fact that a clip feeds a magazine and then the magazine feeds the weapon is hardly as different as football or baseball. While the difference is relevant to a discussion of gun mechanics it is not relevant to the sorts of discussions people usually have about guns.
You know damn well what someone would mean if they talked about being in favor of bans on high capacity "clips". The fact that they're using the wrong word doesn't change the validity, or lack thereof, of their argument. In contrast, misunderstanding about what an assault weapon is or what semi-automatic means is relevant to the arguments being had. I've honestly heard people say something to the effect that semi-auto means what I can only guess they equate to burst firing.