They're using the volume reported by CoinMarketCap which is in turn based on the volume reported by exchanges that fake their volumes. Real volumes are a small fraction of what is reported on CoinMarketCap. This is just bad reporting by a journalist far removed from the industry.
openmarketcap.com only shows reputable exchanges but there is still a lot of legitimate volume on Chinese exchanges faking their volume such as Okex or Huobi. The real volume is somewhat more than what is reported there on the spot market but not more than double.
In addition to that, one could add the volume on the futures markets which dwarfs the spot market.
