GST charged on international in-flight drinks

Jetstar's website says "Card charges on flights which operate solely within New Zealand will be in NZD. All other flights will be charged in AUD. Prices on Australia and New Zealand domestic flights are inclusive of GST. No GST applies to purchases on international flights."

Despite this, when we purchased a couple of drinks on our return flights between NZ and Australia, the electronic receipts we received by email showed an Australian GST component! How many other passengers have been charged GST on in-flight purchases on international flights?

New Zealand-Auckland
Australia-Gold Coast