We have, according to another commenter, what cloud actually refers to: "Cloud kind of means that it's a service hosted somewhere on the Internet, that you don't control directly"

Which is what, back when network diagrams were still cool, would have been drawn as a a cloud — something that your network depends on, but something whose details don't matter. And what one would have called a cloud if they were talking about said diagram.

The word didn't magically appear out of nowhere. These services were named cloud services because that's what name we had already reserved for them.