At this late stage in the ethnogenesis of the Germanic peoples, there was still this ethnic division between nobles on horseback and the locals on foot.
The Yazygi were in Pannonia at the time. http://en.wikipedia.org/wiki/Iazygi
It should be expected that there was some mixing of Quadi and Yazygi from Pannonia which is what the quote from Annales seems to point to, especially after Vannius' defeat, the collapse of his state and their resettlement in Pannonia.