inflation is expansion of the money supply
Let's take this one example. In Macroeconomics 101, there is the formula: MV = PY
M = money supply, V = velocity of money, P = price level, Y = real GDP
So an increase in P (inflation) could be many things, not just an expansion of M (money supply). Even your knowledge of the model is wrong. How much more so your understanding that reality demands more complex models as the reality you're investigating is more complex.