A Donkey Vote isn’t the same thing as an Informal Vote. A Donkey Vote means simply numbering the candidates in the order they appear on the ballot. In other words, a thoughtless vote that any donkey could do.
This is why there’s a benefit to appearing in the first spot and why the impartial and independent Australian Electoral Commission (another invaluable aspect of Australian democracy) randomly determines candidate order.
For the uninitiated: https://www.youtube.com/watch?v=vZ9myHhpS9s