If you watch the video you can see tugs moving the boat. Current speculation is that the tugs/harbor captain messed up and the ship got away from them in the tide and drifted backwards into the bridge.
Sal Mercogliano — a maritime historian at Campbell University - saw indications that the ship's engine may have been stuck in reverse.
See video edited from his livestream here: https://www.youtube.com/watch?v=l2p9bYfFhHE