Their physical appearance rules out certain minorities but not others.  Their clothing, however, is typical of that worn by Han Chinese of their age in their day, and most people would pay as much attention to clothing as to physical appearance.  Clothing, of course, is a very complex medium for conveying information about ethnicity, as it also carries messages about age, class, occupation, interest in fashion, and even politics.  For more on this subject, see the unit on Clothing.