The black shirt does kind of look photoshopped around the arms and neck. Although The Rock does do stuff for Unicef, so it's plausible he'd turn up if the United Foundation was doing something in America. Plus there's a shadow behind him and the rest of the shirt looks as if it's being worn, not from a display or anyhting.
Two things strike me: Why would anyone photoshop The Rock to be wearing a United top; Is that our away kit?! Yum.