As a Russian living among Greeks I can not say that I experienced any unusual rudeness. But yes, permanent smiling may be considered to be deceptive and insincere by some Russians.
But anyway: people tend to express themself in many different ways. It is great to be tolerant to others, while trying to be polite and culture-aware yourself.
The interactions I had--some of them, I should add--in Greece were combative from an American perspective and not a Russian one. If the scenes described in the link are typical of Russian life, then the Greeks I encountered indeed probably would not strike a Russian as rude.
But anyway: people tend to express themself in many different ways. It is great to be tolerant to others, while trying to be polite and culture-aware yourself.