I was reading Nicolae Jorga's "History of Ottoman Empire vol. 1" and he gave an information that, Mete Khan who freed Hsiung-nu people from the rule of Yue-chi, was a servant of Chinese Emperor. But at the bottom of the page there is an editorial note saying, "During the time of Mete Khan, Huns were not serving China" The common sense about Mete Khan is, of course he wasn't serving China but from where did Jorga have the idea?
The current Wikipedia entry for the Yue-chi depicts them as being mostly friendly trading partners with the Chinese. The (likely Turkish) Xiongnu empire built by the victorious Modu Chanyu (aka: Mete Khan, or "Brave Khan" in Turkish), was anything but.
It wouldn't be too surprising to find that histories sourced mostly from the victorious Turks are a bit dismissive of the losers. Relatively friendly trading relations would be just enough of a germ of truth to build the story around.