I don't think that is a GLOBAL EXPLORER Fare.
The LHR-JNB-HKG-LHR = oneworld Circle Trip Explorer
http://www.oneworld.com/products/type.cfm?ObjectID=3
No Travel to the USA is allowed.
Whereas Global Explorer = RTW fare but different to the XONEX fare, it is mileage restricted. Don't know why people bothered with this Global Explorer fare as it is usually the same price as the XONEX fare