"Shoe box" defines a purpose-built container, which continues to be shoe box, regardless of what you put in it. But "vacuum" defines what is (or specifically, isn't) in a container, but in no way defines that container. A shoe box is not altered by its contents, but a vacuum is. We tend to think of a vacuum as a space that's devoid of air, but that's an error. It's a space that's devoid of everything, So putting ball bearings in a sealed vacuum negates it as an actual vacuum, just as much as putting air in it.