I think it is grown in Nth NSW, which is subtropical, with rainy summers.
This page says
Cool, Temperate, Sub Tropical, Tropical. Requires a dry season to produce fruit.
Temp range -7 to 48°C / 19 to 118°F
Quite happy in most soil types but thrives best in a moist, well draining soil. The tree is drought tolerant once established.
https://theseedvine.com.au/product/aegle-marmelos/