The historical usage of the term inflation is, I think, related to the Quantity theory of money.

Quantity theory of money https://en.wikipedia.org/wiki/Quantity_theory_of_money

Of course, today when the media and government is talking about inflation they are really just referring to "price inflation".

That being said the meaning of a word can change over time, or it can have different meaning between two different people based on their bias, or even just their perception of the word.

But your point is taken.