we can tell you are confused
this is just a carrier update for t-mobile customers if you insert a t.mobile sim to an unlocked gsm phone it'll get this update, all carriers around the world get apple update carrier files, they configure specific values for each carrier, mms settings, lte, apn settings etc...
Guess I wasn't clear enough. I have a factory (not AT&T) unlocked iPhone 5. The stuff I read made me believe that only the AT&T unlocked iPhones would receive the carrier update.