Cool example, but all r3f is doing here is just providing the threejs camera, controls and the text with emoji, the watch itself is loaded as a .glb file, where I'd assume most people would be interested in learning about.
The reason you'd use gltfjsx (which that example doesn't) is to have fine grained controls for every node in the scene graph. In the case of the watch, this would map to having a component for each mesh or gear, which can be controlled with mechanics/physics.