Ностальгия or Fellings of nostalgia

I remember a conversation that my father recited few weeks ago after he'd encountered a man of Russian descent,who was born on American soil. After getting acquainted the man remarked to my father that he was Russian. To which my dad responded with inquisitve reproach "Are you really Russian?" The man replied "I am." My dad asked then "If you are Russian, do you know what Ностальгия (rough translation for Nostalgia) is?" The man replied "No, I don't know and I've never experienced that feeling." My father quickly concluded "Then, you are not Russian."
A friend of mine who left his home 13 years ago and lived in the U.S. for the majority of his adulthood does not consider his cozy life in west coast as being an authentic home. When asked about his experience he seems to question his pragmatic choice of life on most occassions and still holds strong belief that his home is somewhere far away. Is this the famous Heideggerian eternal feeling of homelessness?
On the next instance I must admit from my personal experience that I never felt more Mongolian in my life than now, after moving abroad. The feeling is so overwhelming that it lead me to conclude whether special status of being on self-exhile, having diasporic existence, naturally makes me a staunch nationalist; that is existence of identity threatened by surrounding alien idenitity. And to think about Mongolia's national pride and fetish with any national element presupposes me to think that such feelings are at its zenith when we are most open to our neighbours and when we are at most exposed and transparent to the world.
What is exactly nostalgia? Does it have any worth or value to be even mentioned on global level, particularly today in our current state where just yesterday everybody was rejoicing in opening of the borders?

However, I see myself as being unable to argue for the majority of Mongolians out there. The hybrid education that almost simultaneously oscillates between artificially acquired, Russian education, and naturally absorbed nationalism towards motherland endlessly require to level my identity. Where does this thought lead? I said Russian education that I received encourages unnatural sense of belonging, in a sense that I've never stepped into a Russian soil after my birth and into my 1st year and afterwards. So, naturally the Russian culture should be as foreign as any artificially acquired knowledge such as English? Does having been raised in certain geographical location entail certain role in the formation of identity and furthermore nationalistic views? Or, how does certain memory affect one's identity?

On the other hand I must admit that my Russian education was dissimilar to any language acqusition process here in the States. Since early age of 6 I was forced to memorize Russian poems and songs by grandmother. Of course to my family knowledge of Russian language carried guaranteed future entry into prestigious schools and universities in Russia. This process of acquisition in its order re-inforced me to imagine my identity as outside of pool of other children attending regular Mongolian institutions.
My experience might be regarded as intimate with Russian language but the feeling that I have is still dichotomous; although I am sensitive towards Russian culture and the particular elements that are supposed to invoke sense of belonging to Russia such as popular songs I used to sing in school or cartoons I grew up with, on the contrary, almost instantly interpreted into feeling of nostalgia for Mongolia. The memories are mostly constructed around my extended family, evenings spent in front of TV watching Russian chanels, school years and etc.