Interesting theory about
Dryer Coins, but the Australian penny is much bigger in diameter than the American penny, nickel, dime or quarter. So a
Dryer Coin is improbable. Having said that, getting stuck for a long period of time in some kind of mechanical device is certainly possible.
I was hoping that someone would have seen this kind of "shape change" on an Australian penny and how it happened. In the meantime, I'll keep exploring.