I've seen another make scope that adjusted as yours does. Was not aware that Winchester ever marketed one like this. The optical principle involved with focusing a scope is that the nearer the object being viewed the further back in the tube the image is formed. The sliding tube contains the ocular lens, crosshairs and erector lens. Focusing is as you describe by sliding the assembly in or out to bring the erector lens and image into the same plane.
For what it's worth Fecker's adjust by moving the erector while Unertls/Lymans adjust by moving the objective lens, Accomplishes the same thing. Puts the erector and image in the same plane.
                                                 Rich