Yes the Code Talkers were Native Navajo. They used a word from their language and matched it with a letter from our alphabet, much like the NATO Phonetic alphabet (i.e: Alpha = A, Baker = B). They also used code words, for example, turtle in Navajo was 'tank'. Unlike other, more obvious, codes, the Japanese could not decode this. The code was kept so classified, the heroes of the Navajo were not recognized until the early to mid 90s.
Sorry, bit of a history geek here.