The bulge at the drive side of the hub is another way to tell that it is a cassette/freehub setup.

When you put it back don't forget to grease the threads and to torque it adequately. Typical Shimano specs are 260-434 in-lb (22-36 ft-lb or 29.3-49N-m). This is a surprising amount of force, I recommend the use of a torque wrench.