Do you mean that the whistles sound like the Turkish words that they represent?
I tried to "whistle Turkish" and "whistle English" and noticed in English, ambiguity emerged rather quickly. But with Turkish, words weren't as ambiguous.
First the sentence is said in Turkish and then "whistled" and I can hear the same sentence in the whistle. The way that it goes up and down, and the way that he stops and starts mirrors the words exactly and I can hear the words in it.