Doesn't the supply of stuff also matter? How about people's expectations of future prices? How about global-market linked prices of economic inputs, foreign money supply creation? Etc.
I think I could come up with 50 reasons why prices might increase if I sat down long enough.
Yes, understand what the parent is putting forward is a fringe theory. Some schools of economics like Austrian economics are obsessed with the money supply and ignore other factors that clearly matter a lot.
> How about people's expectations of future prices?
These also matter.
Now ask yourself how they matter. Any fall in the value of money must come from an increase in supply or a decrease in demand. If we expect future prices to be much higher than they are now, we will seek to hold less money (because its value in the future is lower) and this drop in the demand for money in the present will drive down the value of money in the present.
Oil prices going up and causing food prices to increase is not inflation.