Einstein is basically consider to be the stereotypical genius in pop-culture; it's not so much the details of his work that's important to the weirdness here, but that he is widely known for having been brilliant. (Consider common phrases like, "I'm no Einstein, but ...") The fact that he is unfamiliar with Einstein is like being unfamiliar with King Tut or Mozart or George Washington; at least in the US, you'd expect most people to recognize the names, even if they might not remember all the precise details about them.