We may never know, maybe they are secretly buying or used other institution to buy and leverage on bitcoin. Those guys behind are not that stupid to let this pass and not book a profit.
We have seen JP Morgan did it in the past, so I wouldn't be surprise if Goldman Sachs is another bagholder we didn't know.
There are indeed many ways that a big institution like Goldman Sachs can participate in this growing marketplace with no need to acknowledge that they are. One day we will just wake up that they are actually raking in profits from their cryptocurrency exposure. These people do not have an obligation to report everything to the public but to their shareholders alone. They can smell an opportunity from mile apart...like a shark smelling the blood.
really tend to proclaim on each action they made which would leave out questions on our minds that they might not or might involved on sudden price spikes.
We wont really know on whats behind but we cant really deny the possibilities of their involvement.