You can't disregard that there was a buy of equal magnitude...

You can't disregard that there was a buy of equal magnitude simply because the buyer chose to place their order in the order book rather than execute immediately at the market offer. Somebody still bought an equal number of shares and someone sold an equal number, it's illogical to argue it could only be one or the other. Like I said though, unless you can interview the buyer and seller, it's pretty useless information. Someone had their own reasons to place a large buy order, just like someone had their own reasons for place by a large sell order.