You are looking at unsettled contracts vs the settled ones. If the settled contracts is very small and the Open interest that day balloons for no aparent reason ie. news. It could be that someone knows something ahead of an event.. Not always, but sometimes. Also, you can have a ton of Open interest and that number wont show in the settled as it was just actively traded that day.. If the numbers dont jump on the settled contracts someone could have just been trying to manipulate the stock price that day with options and flipped them out with no intention of staying.
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