I don't remember what the articles said, I think it was some kind of mechanical failure, that sequence is usually very purposeful and both pilots are ready to respond which makes that swerve seem like it must have been from some mechanical failure.

It is also possible that the protocol here is if something throws the entire aircraft off heading right after the front wheels touch down (with the rear wheels already rolling on the ground) to regain control of the aircraft and then slowly turn the aircraft as minimally as possible while slowing down. They don't necessarily know what the problem is or maybe it is difficult to predict how it changes the feeling of the aircraft's control responses so who cares if the tires get dirty in the grass it is better to just apply brakes and slowdown.

Once the big initial jerk/mess up happens, this is probably the safest thing to do even though "it looks worse" than if the pilots had quickly corrected the aircraft. It would have also been even more uncomfortable of a maneuver for the passengers too whereas in this case it just looks scary because the plane isn't where it should be.

edit watch how the back wheels striking down torque the aircraft in a pendulum like way to the right and then as the front wheels touch down the equal and opposite pendulum swing in momentum to the left occurs which is what throws the aircraft off the heading of the runway. At that point trying to fight the pendulum swing rather than just head off in a tangent straight line is probably safest if the pilots have the space to do it.

edit 2 I wouldn't be surprised if the grass either side of the runway is supposed to be low friction enough that the wheel on the runway's friction will tend to pull the aircraft gradually back onto the runway as the wheels still on the runway have more friction/drag. This is again a method that would work even something had gotten really messed up with the controls related to landing or you suspected in a moment of confusion that this was the case.