Nonconformists would include Baptists, Independents, Congregationalists and so on. (Methodists and Unitarians, maybe, depending on who you asked. Definitely not Catholics or Orthodox Christians) I think the original point of the book was that the term could be used as a sort of double-entendre, but I'm really doubtful about whether it could have applied in the example given.

Anglo-Catholicism has lots of associations with queerness in a British context. Nonconformity? Not so much.