He probably still does. Off the books of course.
He worked for his country. Ambassador to China is a sensitive and vital position. With Huntsman’s extensive knowledge of the Far East, Obama probably thought he was being clever. Give a potential rival the post, clear him out of the way as a 2012 obstacle to re-election, AND look bi-partisan in the process. Hasn’t quite worked out that way though!
He was also Ambassador to Singapore under President George H.W. Bush, of course.