So somebody dumps 75k shares during the last minute...
Yeah. While I havent watched trading in TUES at all, its not uncommon for a trader to "work" someones large order during the day and then near the end of the day or shortly thereafter, show a print for the the total.
For example, suppose a market maker sells 10,000 shares all during the day. (or any number) at various prices.
Then, just tallies them up & shows a print to buy them from the party he was selling for. Less an agreed upon per share commission.
Just another reason volume can often be double or triple counted.
The above can happen even when a firm has their own trader work their order.