That's actually an interesting point. It's possible that people on BTC China are not in fact moving their bitcoins out of the exchange and selling them on another exchange to launder money. They're possibly holding bitcoins in their BTC China wallets. Those transactions will not influence the over all bitcoin transaction volume.

Furthermore, per exchange volumes have been insanely high over the past few days. See: http://bitcoincharts.com/markets/

What you basically pointed out points towards the premise of the article being false. It's not money laundering, it's something else.