it is also to do with the style of songs the singer is singing ,a jazz singer is a jazz singer because he sings jazz songs in a jazz manner?style.
a traditional singer is a traditional singer partly because he sings traditional songs , if he had learned his songs orally from his family and they had not been traditional songs he could not be a traditional singer, supposing he had learned country and western composed songs, from his family orally that would not make him a traditional singer