It will be the people who placed BTC directly into the multipool hoping that the first round of payments would come in at 1 satoshi per ShareCoin (as the dev did mention early on in this thread (he said he would start at 1 satoshi and increase the price)).

A lot of people thought by placing a few BTC in the multipool, they would get a large number of ShareCoins at 1 satoshi each, and dump them instantly gaining a huge profit (if the coin rose to 2 satoshi per ShareCoin, you would double your investment). However the dev didn't sell them to the multipool at that price and so people are just selling at around the price they paid for them just to get their BTC back.

That's my theory anyway.