Best regards to a Capesize sailor.
We burned just over 100 tons of fuel per day if I remember (12 years ago)
When you change out ballast you are taking a full pressed up tank and emptying it to where you have "free surface".
The water in the tank can flow back & forth across the tank.
Free surface alone reduces you stability. As you remove more ballast water from the tank your stability is reduced more.
I had a carefully calculated process of emptying a minimal number of tanks at a time (max 2) and then refilling those tanks before I went to the next set.
I'm guessing they didn't calculate there ballast exchange & took too many tanks down at once. From the pictures it looks like they just tried to pump it all out at once.
I have found that a lot of the people ashore sitting at the computers that load the ships know little about stability.
Ocassionally you find an ships officer that doesn't understand it either.