I doubt that it's just interest rates as not all capital cities are currently experiencing sales or price growth (might be a different view in Sydney), and there were some areas that were surging even when interest rates were higher a few years ago.
Population growth, economic growth and infrastructure investment all play a role. Those are all demand side factors though, they don't tell us anything about supply.
Most of Brisbane's (and Queensland in general) population growth traditionally comes from interstate migration rather than overseas arrivals. New South Wales traditionally bleeds quite a consistent flow of people north over the border.
