More generally, how can a piece of music be made to sound, for want of a better word, foreign?
The answer is: both technical means and local culture (and its characteristics) produces a certain idiom of sound.
First, it is important to keep in mind that the Western music system of today is an about universal system which has developed over many centuries, which consists (so to speak) of an extensive toolbox and means of expression to compose and play music.
With this toolbox, many styles of music can be created.
The creation of folk music, which is not necessarily national (as nations arrived later on the scene), but locally produced music, did not proceed using the extensive tools and rules of this advanced Western toolbox. It was thus created using a limited toolbox of means (scales, rhythms, harmonies and instruments). Secondly, probably we should not think too simply in terms of means being the cause, but a correlation of means and temperament, the character and culture of a people. Limitation and exhaustion of a limited amount of means, combined with local preferences, local temperament and character, and limited means produces thus typically recognisable forms of music.
Imagine for instance that at the time the orchestra and its extensive toolbox of instruments which allows for a much greater range of expressions was not yet developed. Limited means thus also implies a limited amount of instruments, with a limited range of possibilities of expression, and again exhaustion of the possibilities of limited means leads to a pronounced character (in the context of local temperament of the people in question). Add to this, spontaneity; the non-precalculated (like much modern music often is). There are recognisable patterns which spontaneity forms on the basis of local temperament.
Also, take into account that many folk melodies were not composed on the basis of the Western general tuning system(s). Many folk melodies and harmonies when converted to be played according to the rules of the Western music system and its instruments, are approximations of the original. Hence, the niche of musicians who use original instruments and tuning systems, trying to approach the original idiom more closely. Nevertheless, the vast and more universal toolbox of the Western music system can approximate the original close enough, and our ears are more used to it.
In short: limited idioms or biotopes, producing the very characteristic with its own riches. It is a paradox perhaps that a more comprehensive universal system produces less of the peculiar characteristic, and that does not only apply to music.
Some of the Western composers where geniuses in trying to 'recapture' these idioms, to capture their spirit using the more universal tool box of the Western music system.
"The master shows himself in his limitations", someone wrote. The art of the real master therefore also has a unique stamp on it, just like folk music bears the unique stamp of a small collective through its limitations.