I’m pretty sure you are supposed to declare agricultural products at customs. Sure, if the apples are cooked into a pie that’s probably fine but I believe most countries don’t let people bring in fresh fruit because of the possibility that some pest (insect, fungus) could be hitching a ride on it.
I believe the point is that in other countries they won’t rifle through your bag to verify whether or not you have brought apples. I’m not familiar with Australian customs though so I could be mistaken.