That doesn't really matter.
The point Turnbull was making is something along these lines: https://xkcd.com/538/
No, they can't change the laws of mathematics to make all encryption have a government backdoor. They don't have to, though. They can just legislate to make use of non-backdoored encryption criminal. And if they want to make generating random streams of bytes a crime they can probably do that too.
It's not idiotic, it's authoritarian.