Unfortunately, the best advice that I can give you is to try calling them again and asking what fare class your flight books into. N = Basic Economy; everything else is not. I can confirm that the BE fares on that route do have the USA-only sales restriction. If I put Beijing or HK in as the sales city on ITA Matrix, I get the US$100 fare as the lowest available for that flight. Now, there is a US$90 G fare filed, but I don't see any G availability on that particular flight (regardless of point of sale) and US$90 is still more than ¥569. So... I'm stumped.

Sadly, I still can make neither head nor tail of the display of fare information on their website.