I think that you'll find the author meant that if the number of dollars doubled, with all else held the same, that the currency would go down by roughly half.

I think that you'll find the author meant that if the number of dollars doubled, with all else held the same, that the currency would go down by roughly half. M0 doubling over ten years is not surprising if the underlying wealth that it measures also doubled, and doubling in ten years is on the right order of magnitude. Of course, there are also other factors at play, so it would be unlikely to map exactly to the inverse of supply, but as a good rough first order approximation, it works OK.