The exterior receptacle shown in the picture was found hanging out of the box. Why? So the white wire connected to the ground terminal could be routed around the corner and attached to the hose bib. Neat idea - huh?
My guess,the mounting screw rusted off. That is what the ear looks like in the box
Is this a house with a grounded wiring method? If not this may be the way they decided to ground the receptacle.
Given the color of the wire and the mounting ring I would question if this was for the phone system.
I agree and think it may have been for phone at one time, but during the recent homeowner ‘flip renovation’ he decided to reuse the ground for the receptacle. Many other receptacles in the house had no ground at all.