User blog comment:Callofduty4/Black Ops II receives large title update/@comment-25496444-20121207195554/@comment-3967954-20121208000030

'Alternate reality' doesn't automatically mean that everything in this reality cannot occur in the alternate reality. An alternate reality, such as the CoDverse, is a reality in which the events of the world we live in still take place, but in a different way.

You might as well ask "If it's set in an alternate reality, how come there are humans in it?".