As a former beekeeper who kept them for many years, I will say that the man is wrong. You can identify killer bees because they build comb in the open, without any protection. They'll also build in old tires or on the ground under old wood or metal piles. Colonies that do this won't survive the winters in the north. All bees swarm in the summer. Telling someone to kill a swarm is stupid. I kept swarm traps out in the summer to catch the swarms I missed in my hives. Keepers who take their bees to California and other warm climates for their pollination seasons have had their bees pick up some genetics from the killer bees they brought back to the Midwest, but once they return home, the killer-bee genetics are bred out quickly. Those of us who bred queens would also quickly eliminate the ones producing hostile bees. No reputable beekeeper would tell anyone to kill bees indiscriminately.