It is auto-redirecting to the @types/three package and getting the types from DefinitelyTyped. You can see that in the breadcrumbs, but it might be something that could be better highlighted (and maybe even redirect the URL to make even more obvious to developers).
https://tsdocs.dev/docs/three/0.159.0/classes/Bone.html
It’s fun to just read through all of the different entities in the 3D ecosystem, even though I’ve only used it only a couple of times.