I was unaware Keynes write about Lenin's schemes right around the time the Russian Civil War started...it appears he was spot on as he was with many other theses...In Chapter VI of his 1919 book, The Economic Consequences of the Peace, Keynes wrote:
"Lenin is said to have declared that the best way to destroy the Capitalist System was to debauch the currency. By a continuing process of inflation, Governments can confiscate, secretly and unobserved, an important part of the wealth of their citizens. By this method they not only confiscate, but they confiscate arbitrarily; and, while the process impoverishes many, it actually enriches some."
Origin and Historical Context:
Where Keynes got it: Research by economists Michael V. White and Kurt Schuler shows Keynes likely based his opening line on reports of a Spring 1919 press interview with Lenin published in London and New York newspapers. In that interview, Lenin was reported discussing hyperinflation as a deliberate strategy to undermine the purchasing power of the middle class and collapse the capitalist pricing system.