It was pretty obvious that it was a yellowed controller even you could have figured it out. Especially since in the bottom pictures and even around the edhes there are some grey spots.
If it truly were a gold controller you would not find any grey spots since i highly doubt they would have painted the controllers gold but made the plastic gold colour if it were a gold controller.
Also, that controller has definitly seen some better days and I'm not talking about the yellowing.