Karma:

I have nothing to say one way or the other about the origins of Tamangs.  They might very well have come from Mongolia as the author mentions or just have descended from Tibet as you asserted based on the etymological clues.  I just found it interesting because it segues from Prashant Tamang's success to the "bidambanaa" of Tamangs in general in Nepal. 

Above article is written by a well-known journalist in Nepal, Kanak Mani Dixit, as it is noted at the top of the posting.  Perhaps your concern would be better served if you write to the editor of Himal magazine where this piece was originally published.  I apologize if you felt slighted in any way.  Thanks.