Maggiesdad,
I saw the same presentation here in N FL. The usurpation looks like a swarm moving into a hive. The bees land like a swarm and then move in.
It does sound more like robbing. In the initial stages, look for bees fighting, often 2 bees falling to the ground together. Later after they kill the queen and break the morale of the home bees and are free to rob it out.
Jim