Keynes had argued in his book Indian Currency and Finance that whether a central bank holds its reserves in gold or in foreign exchange "is a matter of comparative indifference," and that "in her Gold-Exchange Standard
Under the Bretton Woods agreement, the dollar would remain on an international gold-exchange standard
(meaning that dollars could be redeemed for gold, but only by international traders), and other currencies would be convertible into the dollar.
Ahamed does to history is to fail to distinguish between the flaws of the classical gold standard, on the one hand, and the far deeper imperfections of the gold-exchange standard
(so similar to the evils of today's dollar standard), on the other.