Food can make a dog salivate without any training. In Pavlov’s experiments, a separate cue was repeatedly presented in association with food. Eventually, the cue alone could produce salivation. This learned association is called classical conditioning.
The important change is what predicts the food. The animal is not being rewarded for choosing to salivate; an existing reflex has acquired a new trigger. That distinction helps separate classical conditioning from learning through the consequences of an action.