I thought that looked like a '35 drum, but since I couldn't see a side view of the outer surface of brake shoe contact area, I wasn't 100% sure.
Also, all the rear '35 drums that I own have the separate two piece hub/drum construction held together by sweged studs....except for the open style "Rockey Mountain" type '35 rear drums which are of the one piece construction.
If that drum came off the tapered axle that easily, the tapers of drum hub and axle were not mating properly, and/or the axle nut was not torqued down correctly. Just sayin'