A hardtail Cafe racer is an oxymoron. It's two terms that cannot co exist peacefully. A Cafe racer by definition is functional and a hard tail is not so much. More importantly this is a really bad example of focus on what looks cool without any real engineering input.
On smooth roads at low speeds that bike will probably be fine until it's sold or taken a little faster around a corner and cornering forces bend or break the swingarm and the bike lurches out of control. It's easy to call "Darwinism" but Dave clearly tried to brace the swingarm to stop it moving. Unfortunately it's not designed to take the forces that it will be subjected to and he wasn't to know that or how dangerous that bike is.
The real question is what he can do with it now.
If he wants that "look", he needs to engineer in a single shock rear end. If he wants it as a hard tail, it needs to be braced. His choice, but that bike should not be ridden as it is IMHO.