Someones sold to get quick profits - and to keep the course low.
They also have such volumes, which bring enough dollars to them. I.e. big owners.

Or
someone's robot had a bug


It looks like that there was no sensible reason to start selling.
Especially when the course has finally started growing after being for awhile at the 10 month's lowest.
Who wants to sell in such a rise?  Owners, who want to keep the course low, or who think that the course will go to 100 dollars.