If that's true, then Rush's audience is dumber than a million Fredos, which makes Rush pretty stupid for not thinking of that.
Obviously the guy didn't believe that Fredo was Cuomo's real name, otherwise filming the set up would have been completely beside the point. The point was to get the reaction on film.
Rush didn't invent the Fredo meme for Chris Cuomo. It's been out there at least since 2010 in New Yawk City, thanks to Curtis Sliwa.