[thelamest]

This is not the common definition (cf. https://en.wikipedia.org/wiki/Inflation), but a narrower one (https://en.wikipedia.org/wiki/Monetary_inflation). Semantic difference, but one that remains a little confusing and harkens back to old economic debates. Focusing on policy causes of price changes is preferred among authors who want to tie inflation only/mostly to central bank actions, but mainstream economics, with Friedman etc., works with a slightly wider model (money supply is a key lever, but other things matter as well).

[yyy888sss]

Defining inflation as rising prices is the newer, MORE narrow definition as measurements such as CPI are capturing the downstream effects of a fundamental cause (creating money).

[whimsicalism]

Inflation is and always has been about changes in the price level. If velocity halves and money supply doubles, there is no additional price level change - so it is not a "fundamental cause."