the drum and hub are two separate pieces held together by swaging the lug studs. The axle/hub are tapered with a square key to keep it from spinning.
they can be a SOB to get apart even with the correct puller. it is a god idea to keep the nut at the end of the threads as the axle will mushroom if really stuck. it also prevent the assembly from ejecting into any nearby object

Once a lot of pressure is applied, smacking the end of the puller and around the hub itself will sometimes vibrate things enough to break the bond between the tapers. A smoke wrench with a rosebud tip also works.