Qaḍāʾ replaces a particular invalid fast with a later fast. Kaffārah is a separate, additional expiation imposed only in specified cases. They are not alternative names for the same duty.
The source refers to the expiation of ẓihār. In classical Hanafi law, this is described in a sequence: manumission (a historical institution), then two consecutive months of fasting when unable, then feeding sixty poor persons if unable to fast. Applying the sequence in an actual case requires qualified case-specific guidance.