Thank you for confirming my hunch that this level of confident-incorrectness and mixed up history could only have come from some damn article on mises.org.
While it may be true that the Austrian school uses it like that, it's certainly not the case that they're the only ones. In fact, I suspect if you speak to anyone economically trained over a certain age, there would be a high chance of them defaulting to this.
Growing up, a close relation of mine was an economist, and certainly not of the Austrian school. As a teenager, I was basically ganged up on by a teacher and some kids when inflation was brought up in class. They seemingly had no concept of monetary inflation, and I was forced to swallow that it referred solely to prices going up. I obviously questioned him on this incident, and he outlined that the "prices are going up" phenomenon is price/consumer inflation, and that increases to the money supply are monetary inflation.
Historically, monetary inflation and consumer inflation coincided (Supply of X goes up -> X is devalued -> consumables are now charged at higher X), and so distinguishing between the two wasn't particularly pertinent.
The Roman Empire's observations that debasement of their coins resulted in the increase in prices, meant that the original conception of inflation really was as a monetary phenomenon, not just that prices are going up.
It's really only a relatively recent phenomenon, from the early 20th century, that you had dual definitions trying to occupy the same word, although the concept that price inflation could deviate from monetary inflation probably was starting to be understood with the establishment of price indices in the 19th century.
Keynes arguing that prices could rise independent of the monetary supply post-Great Depression increased the focus on consumer inflation. It was around the 1970s where inflation more commonly came to consumer inflation in academia. 'Stagflation' of the 1970s is probably the tipping point in usage.
To conclude: it's not really wrong to use inflation to refer to monetary inflation, as it's the original usage, but considering consumer inflation as 'inflation' is definitely more in fashion (especially in the US).
