Truth be told, the Nangong Family could probably put on a good act if they wanted to, but they likely considered that their young members would eventually be put to use anyway. Therefore, they didn't bother to invest much effort into their education. The Xiao Family, with a longer heritage, probably had more comprehensive domestic teachings, making sure to appear diligent on the surface.
The King of Zhen Country probably wasn't genuinely virtuous and loyal either, but simply played the part of a benevolent prince for the sake of his clan. His role was merely to handle the public relations, showing no real sincerity like that of a devoted visitor persistently seeking wisdom. Otherwise, why would his attendants, even in such a remote wilderness, still classify visitors into ranks according to the invitation received? I fear that on Xiao Family's own territory in Zhen Country, they'd be insufferably arrogant.