At a broad conceptual level, and in my view in practice as well, this conclusion is clearly mistaken. Indeed, under a fiat (that is, paper) money system, a government (in practice, the central bank in cooperation with other agencies) should always be able to generate increased nominal spending and inflation, even when the short-term nominal interest rate is at zero.
The conclusion that deflation is always reversible under a fiat money system follows from basic economic reasoning. A little parable may prove useful: Today an ounce of gold sells for $ more or less. Now suppose that a modern alchemist solves his subject’s oldest problem by finding a way to produce unlimited amounts of new gold at essentially no cost.