Looking at that video, a heck of a lot more than a hundered birds fell. Most took off again. Did they die from hitting the ground from 50 feet up? If so, I'm guessing the birds were all affected by some sort of electromagnetic disturbance. Migratory birds are very sensitive to such things.
It was a flock of blackbirds. They have a dynamic all their own. This one hit the ground. Some died.
Maybe they fly in formation like the Blue Angels, and the lead bird screwed up or died in flight. I have birds running into the front window of my house quite frequently. They do misjudge a lot, giving rise to term “bird brain”.
Typically they follow a leader and unfortunately this leader led them into the building and ground.