The African bees guard their hive aggressively. If you encroach, the sentinels will fly into you to give you a warning (that sounds like what happened to this lady: she got hit by bees buzzing around her before the swarm attack). If you continue closer to the hive, you will then be attacked.
The correct thing to do is to take notice of the warning, and reverse your direction of travel. Going back where you came from and finding an alternate route will prevent the attack.
The African ancestors of these bees had to contend with honey badgers, which have thick hides (relatively impervious to stings). So the bees evolved to attack in the hundreds instead of the dozens to vanquish these critters.
Then some people in Brazil cross-bred the Africans with some European honeybees, and then some idiot must have left a door open, the bees escaped and migrated northward, and the rest is history.
Makes sense. Thanks.