Just to keep this up-to-date as this may be helpful for others.
I was in contact with the regulator (CAD) and they confirmed that airlines are not approved to charge fuel surcharges for flights departing Hong Kong, even if they are ticketed elsewhere or in other currency. FYI BA doesn't charge it for ex-HKG flights ticketed in GBP in UK either.
Direct quote: "Our consideration of fuel surcharges was based on the origin of the flights rather than the point of sales. "
The regulator will be in touch with AA directly about my ticket now, we'll see what happens.