Was the claim not "doing n-back helps working memory"? Hardly "become smarter". Whether or not it works is worthy of discussion, but straw-man-ing a hyperbolic claim that wasn't made doesn't add to the discussion.
That was half the claim. The full claim was that it improves fluid intelligence by improving working memory. The title of Jaeggi 2008 is "Improving fluid intelligence with training on working memory".
