Surely there are numerous situations where someone might take their hand(s) off the wheel other than turn signals or gear shifts. What if a drop bear gets in through the sunroof?
My guess is that they aim to identify non-sanctioned actions. They claim to use some sort of machine learning in addition to human verification.
I have no direct experience with them. These are simply the claims made by the authorities when they were trialed.
I cannot recall ever hearing of anyone charged with such an offense, but I am sure you would not pass a driving test if you didn't use both hands.
https://www.canstar.com.au/car-insurance/6-road-rules-youre-...
I am not sure about the cast/sling situation. But I imagine if it was considered a contributory factor in an accident, you would be culpable.
https://www.canstar.com.au/car-insurance/6-road-rules-youre-...
And regarding phones; it is illegal for a driver to be distracted by an electronic device -- even if a passenger is the person using it.
It is quite strict, but the number of preventable deaths with this sort of distraction as a contributing factor is staggeringly high.