Now I am told that snap beans are so called as you said but the opposite is string beans which have to have the string removed and with it they don't snap in half!!
Lots of these funnies with beans. A bit like the runner.. so called because it runs up and away ,like the beans that Jack grew LOL
True butter beans I think have a texture that is less dry than a lima a bit more like the greasy beans.
I enjoy the book The History of Beans which has lots of these anecdotes in.
XX Jeannine