Why does "Original" in the "Root Transform Position (XZ)" not follow the root bone?

I've read the docs and I understand that when "Root Transform Position (XZ)" is set to "Center of Mass" that means the GameObject will follow the center of mass of the character. But what does "Original" mean exactly? What point is the GameObject following? My first thought is that it would be the root bone (hips on my model) but that doesn't seem to be the case when looking at the preview window.