If you right click on a static mesh, you have the option to transform it into a skeletal mesh.
It creates a skeleton and a skeletal mesh.
As you show on your video, with the Skeletal Mesh Editing Tools plugin activated, you access this window that allows you to built the skeleton starting from a Root Joint
I’m interested by this tool because switching the skeleton/rigging/skinning task from Maya to Unreal means doing everything on the same interface.
I’m very interested by the Control Rig creation process of Unreal and animating in engine.
So why not doing the skeleton here as well ^^.
Plus I’ve been thinking about switching from Maya to Blender but I’ve always been scared by the task.
Re-learning moddeling, skinning, rigging and animation would be such a big task 
Whereas, only re-learning modelling and keeping the technical part to Unreal that I am used to sounds better to me ^^