it is always possible that someone with deep pockets, tangentially connected with the creator of Nyan Cat, is injecting money into the site to create the illusion of a large sale. the eBay equivalent of bidding on your own item. there is a huge incentive to do this, because of the hype it creates (large sales = 'art world' news), leading to more people wanting to 'get in on the action'.
Precisely. People have been doing this with plain ol' trading too. But then CMC started cleaning up the volumes and there were transparency reports on exchanges. Before this happened some exchange you never heard of was claiming to be a leader in volume.
There are already so many... call them information games, ranging from ego puffery to outright cons, that I'm surprised bitcoin hadn't infected it already.
Should anyone wish to trade their fungible tokens for my nonfugible, but very pretty, buckets of bits, please hit me up.