If you have people buying and selling nothing that's going to be a small economy.
If you have the same people, with the same wealth, buying and selling stuff to each other, that grows the economy.
If you have the same people buying and selling stuff faster, they may still retain the same wealth but the economy will grow even further.
The size of the economy is about the number of transactions, and printing money or borrowing money can definitely grow the economy (IF that money gets used to accelerate economic transactions).