The greatest difference, to some experts, between other methods and case studies is the distinction between the researcher's (1) beginning by presuming, a priori, to know the relevant constructs and variables, measuring their incidence, and finding out how changes in them may be influenced by other events and (2) entering into an event to learn what is significant in it to the participants.
Some experts think researchers begin by presuming with a case study and other methods start with no hypothesis.