a thought about block trades

snailittle

it seems the block trade  data is not always predictive of market move.
I doubt if block trades  can be used to tell smart money flows.  
Since for every order there is a buyer and a seller, it might be difficult to say that the money is flowing in or out because the way block trade is done is by a single negotiated price between two parties, rather than by tug-of-war between all selling and buying orders on market.  
Also I am wondering sometimes the block trades might actually capture some retail investor actions,  e.g. for all retail investors selling spy using vanguard, will vanguard combine the orders and then sell them as block trades?  Does anyone know the answer to this question?