Transports onload/offloading adjacent to enemy controlled sea zone
I believe you are correct. Australia is adjacent to a hostile sea zone, and therefore British transports cannot load or offload infantry in Australia while an enemy ship is in any of the sea zones around it. I base that on the fact that "territory" always refers to land, where-as "zone" refers to sea.

Seems incredibly overpowered. But that is how the rules read.