It is not exactly what you think it is.
This is obviously a "put through", or broker to broker trade on behalf of two major clients one a willing seller and the other a willing buyer. In cases such as these, because the deal is a very big one, it is handled in this way. The reason for this is that if it were allowed to enter the general market its size would be enough to disturb the market, i,e,. its natural progressiion in terms of the supply demand schedule being progressed at that time. in those circumstances.
As a size of this nature suddenly apperaring is not related to the supply demand schedule currently in progress it is handled conveniently in this way. A buyer has to be found before the seller can execute, or a seller has to be found before the buyer can execute. This occurs outside normal market size, and consequently outside normal market liquidity.