Wouldn't bother me if he was a Muong. Could only be a rumor, but if it's true, it wouldn't bother me.
http://www.britannica.com/eb/article?eu=55...ong%20languageshttp://www.nhandan.org.vn/english/identity/20030621.htmlMuong and Kinh are one in the same. We are two branches of the same people. The Muong and the Kinh were once one group long ago anyways; it's just back then they were a group of Viet people who separated and went into the mountains to live. They have much less Chinese influence than us Kinh do because of the separation.
In essence, him being on our side was like having your brother come in and help you. It's not too much of a weird occurance. I've heard many times in the past, the Muong teamed up with the Kinh to fight the Chinese. They are separate, but still feel a very strong brotherhood with us.
They even look very much like us.
