Apis mellifera scutellata is one of several subspecies of honey bee native to Africa and it is generally referred to as the African honey bee.
It was brought into Brazil for genetic experiments where it was accidentally released into the wild. It was able to mate with local honey bees of European stock and spread rapidly. It is the descendants of this original introduction that we call Africanized honey bees—not African honey bees. We call them Africanized because they are carrying many of the genes introduced by Apis mellifera scutellata, but they are not pure Apis mellifera scutellata—in other words they are not true African honey bees.
Think of it this way: if you cross a poodle with a collie you get a dog that is not a poodle or a collie. Now your particular cross may look like a poodle, bark like a poodle, and have curly hair like a poodle but, trust me, it’s not a poodle. The offspring of this cross has been poodlized.
Same with the bees. These new bees may sting like African bees, swarm like African bees, and chase like African bees—but they are not African bees. They exhibit an overwhelming number of African bee traits so we say they have been Africanized.