You can call it "fake" trading (i.e. buying and selling something, pay just the fee for the trade and create artificial volume).
Or in the case of zero fee exchanges (not Poloniex according to their posted fee rates, but who knows what private discounts/rebates may exist), you don't even have to pay the fee to do it.
I'm not sure about that. A lot of people are following Ethereum, and I believe that the volume is genuine. If I was part of the Poloniex exchange, I would not risk my reputation like that. They have become a leading (not only altcoin) exchange in the world and they are making a lot of money anyways.
