... Gorbachev's success in the West is based on the fact that he became the first Soviet leader who smiled to people in public. Many [Americans] perceived [Gorbachev] as a person who was open to communication and therefore not dangerous.
So how exactly does a smile in America "not mean anything really" when it allows Americans to distinguish people in their society who are open to communication from those who aren't? That's a very clear social function, full of meaning if you ask me.
TL;DR: in American society, smile serves two functions: (1) to express emotion of happiness/satisfaction, (2) to signify that one is "open to communication, while in Russian society the role of smile is exclusively tied to (1). Failure to perceive the dual-purpose role of smile can lead a Russian to conclude that smile has no function at all in American society (not "meaningful"). Similarly, failure to perceive the singular role of smile in Russian society, can lead an American to incorrectly conclude that all Russians are "closed to communication."