Isn't a group of jellyfish called a "smack?" The term "fluther" is made up, isn't it?

Interestingly enough, Wiktionary doesn’t show a definition of “smack” (out of many) as a group of jellyfish, and only shows Fluther as a surname. (Who knew?!)

So, which is it? Why should a group of jellyfish be a fluther rather than a smack? Or vice-versa?

Also, does a “smack” mean “fluther” in another language, perchance?