The origin of the word is completely unknown, so I don't really know if anyone has the authority to claim "it's a backronym" although I imagine it is. We don't know of any good history for the word at all.
surelly the fact that ned predates the term non-educated delinquent is pretty damning evidence. Also there is no such word as non-educated. Both pretty indicitive of backronym. Theres more discussion on the etymology of the word on the corresponding wikipedia article.