Bots are also a cause, but I think that the volumes faked by bots are not that big.
I'm curious if it is possible to trace the volume produced by bots in principle. I mean you will not see them on the blockchain, only as part of exchange trading volume, but then you could expect the trading volume to be forged as well. The bitcoin blockchain seems to me the only reliable way of estimating bitcoin volume and its supposed increase within the last few weeks...
Some bots are not very smart. I've seen on an altcoin exchange something that could help:
Although there are normal sell and buy orders, from time to time transactions are made without touching the existing orders.
For example a Buy order is made at a bigger price than the biggest current buy order and in the same (milli)second the order is also filled.
It might very well be a human mistake. I never checked it myself, but are such orders filled at the current market price or at the price of the order on cryptocoin exchanges? The "real" exchanges out there automatically correct such errors and execute the buy order (for example) at the market ask price at the moment...
I watched this for about 8-10 hours. They may be badly programmed bots made by somebody else, not the exchange. But it was obviously bots.
2-3 times during those hours real transactions were done.
And when there was a big price movement on all other markets, here also real traders started buying/selling.