Actually... irrespective of what it says on the ticket for baggage allowance, the correct allowance is 2 pcs. Once a RTW touches the americas (north or south), you are allowed 2 pieces of baggage at 32kg per piece worldwide. The only exception to the rule is within north america on AA where they restrict the weight of the bags to 50lbs each. But you are still allowed 2 pieces.

The check-in agent may be following the rules.. but you should have highlighted the fact to CX that you are on a RTW ticket and that you are permitted the aforementioned 2 pieces worldwide. CX should not have charged you the excess rate. You have a valid case and you should be able to get a refund. You would of course have to contact CX at BKK airport directly for this.

TG is the ground handling agents for CX in BKK. They are not very well versed in ticketing procedures. Or anything for that matter - but that is a different story.

As per ONEWORLD EXPLORER RULES (on AA's CRS):