The building obscured the reason for the pitch down , might have been an over correction to push it on the runway . Just pure speculation about the brakes as I have seen the results of wild landings where brakes were involved . Usually the tire flat spots with brakes on or blow the tires right out are the biggest clue as to a brake issue .
When the brakes are frozen the tires usually blow . Hence a heavy landing is a recommendation to break the ice if frozen brakes are suspected .
They could have just been practicing or simulating carrier landing techniques . Hard to see the control inputs on that video due to the building .