Thats the way it is in PA as well. If you join the PSEA you also join the NEA.
I have long assumed it is that way in all states-- that the NEA has a racket set up with state organizations in all 50 states, and local organizations under those. You join at the local level and you automatically "get to" join the state group as well as the NEA. Too bad for many teachers they like to keep this a secret. Now people are learning why.