To me, it was like a "rumor" to state that the "urban" shape (compact and bucal cavity driven) nose flute was used for ages by the Guarani people (check this post). They could have begun producing it for commercial reason (difficult for them to survive, nowadays) for several years only. Contrarywise, what about Vietnam? Same (or so) shapes are massively produced in Vietnam : has it been a traditional shape for long there ?
So I asked a famous ethnomusicologist, specialized in traditional flutes, Mr. Randy Raine Reusch (Ethnomusicologist, composer, musician and world-music consultant), who answered gently and quickly...
After having told me that I should not call our "urban" nose flutes "nose flutes" but "nose whistles" (I agree, but the habit has been adopted by all players...), Mr. Raine-Reusch wrote :
« The instrument that you play is originally from the Guaranis people used for calling birds, to my knowledge it was not used for melodies. However, this whistles along with many other native whistles became popular for use in Samba bands in Brazil, and you can easily see them at the Carnival parades. They play percussive parts. The western humanatone and Vietnamese instruments were copied from the Brazilian version. There is no history of these instruments at all in Vietnam, they are just made there for commercial purposes. As well there is not tradition of these instruments elsewhere in the world until the popularity of the humanatone as a novelty instrument, since that time, they can be found as novelty instruments made in a host of countries, out of plastic, wood or metal.
The brazilian instrument is the traditional shape, and there is no record of how long it has been used in Brazil, which suggests that it is longer than when Europeans made first contact. »
Things are clear now.