It's the same as carpentry and sculpting. It's the same thing, but one is a craft and the other is an art. This guy just took time off making furniture to build a sculpture.
Sure, he could have made a new kind of furniture, but making sculptures also has its merits (or not, depending on your viewpoint, I guess).
There are tons of projects that will never go anywhere, done just for learning or as neat hacks, but why ensure that one won't?