While the Media is having a laugh over this there is a good reason for doing it.
An unscrupulous Aussie exporter could try and get around the tariffs by marking his goods as being from those islands and not the Australian mainland................
...or Red Chinese.
but those territories are Australian and under Australia. The islands are a territory (Territory of Heard Island and McDonald Islands) of Australia administered from Hobart by the Australian Antarctic Division of the Australian Department of Climate Change, Energy, the Environment and Water. The administration of the territory is established in the Heard Island and McDonald Islands Act 1953, which places it under the jurisdiction of the Supreme Court of the Australian Capital Territory, with the non-criminal laws of the Australian Capital Territory and the criminal laws of Jervis Bay Territory applying to the Territory
No exporter could get around tariffs as this is under the conditions already put on Australia
Heard Island, by the way, was named for an American, the first person known to have seen the island.