Imagine if the roles were reversed. Every day you're forced to the brink of starvation, practically three paws already in the grave. Then, and only then, does your caretaker finally announce your salvation for yet another day by opening the bag.
If the cat couldn't differentiate the bag by sound, they'd have long starved - either they'd have expended too much energy by walking to the kitchen when no food was coming, or they wouldn't have reached the bowl in time to fend off their untimely demise.
The life of a house cat is a daily struggle against fate itself.