Again, prices are merely a measurement of supply and demand factors involving the two things you’re comparing: the supply and demand of whatever commodity you’re looking at, and the supply and demand of the money itself.
The laws of supply and demand are basic microeconomic laws that virtually no school of thought denies. There is nothing really “Austrian” about it.
In the example you give, you’re talking about a finite supply of goods, and a fixed supply of money. So one of the variables won’t change, and another will only decrease. Now you’ve just got the demand for money and the demand for goods. Those could both increase or decrease. Any change in price could be a reflection of any or all of those 3 pieces.
For example, if prices rise, and the money supply is fixed, yes, this is usually attributable to a decrease in supply of goods. But it could also be a reflection of a decrease in the demand for money.
I highly recommend checking out this beginner post.
As for Dave, here’s a few articles if you’d want to get a little more familiar:
Demand for Money and Supply of Money
Hyperinflation, Money Demand, and the Crack-up Boom
Also, Bob Murphy got into a back and forth with David Beckworth on the subject…
Is There a Conservative Case for QE?
Taking Seriously the Excess Money Demand Problem: A Reply to Robert Murphy