GDP is not "the amount of money in a country".
GDP is the monetary value of goods and services produced within a country during a given period (a flow, measured in dollars-per-year).
The amount of money in a country is a measure at a point in a time (a stock, measured in dollars).
I realize Fortune magazine isn't The Economist, but I'd still expect PhDs in political science opining on economic topics to at least understand the difference between stocks and flows.