the same bitcoin can be sold and bought multiple times a day, hence there is a possibility of having turnover greater than the number of bitcoins in existence. but the tape and orderbook shows everyting clearly, only one thing apart from fake volume can explain this paradox - dark pools on btcchina?))
This and this is often explained as bots fighting together, one selling massive one automatically massive buying and volume is from that.
Fake or not, china is very important in bitcoin world.