I don’t think that was the point, it seemed to me that the other settings were set to Low so he could demonstrate that the only settings affecting tree draw distance were Trees and Terrain LOD.
It’s worth noting that the quality of the trees does not seem to change beyond Medium, which is also demonstrated in the comprehensive graphics guide (though keep in mind the Ultra screenshot is erroneously the same as the Low one). As such, the only quality setting is between Low and Medium, with High and Ultra being mere draw distance boosters (Ultra drawing as far as the loaded data allows). Considering the tiny performance difference on modern GPUs, separating the two probably wouldn’t help much in most cases.