Actually, burnhal isn't far off the mark... iso-pentyl acetate is a chemical pheromone released by the "guard" worker bees (in reality, older bees that have more venom) that are mostly near the entrance to the hive if the hive is attacked. (The guard bees can't yell, hence the pheromone). This chemical release would, normally, incite the other bees to attack as well, but the smoke prevents the release of this pheromone, therefore, the other bees aren't made excitable. Additionally, the smoke entering the hive is sensed by the bees as a prelude to a fire and, in the wild, they would consume as much honey as possible to carry it away from the fire threatened hive. They are busy eating as much honey as possible, which keeps them focused on that activity, rather than attempting to sting someone or something, especially since they have not received the required warning... ingenious, no?
We try not to use to much smoke to enable the bees to recover quickly and stop their frenzied eating activity. It just takes a few squirts from the smoke generator...