As reported on this blog, the human population did indeed shrink as a result of a massive volcanic eruption at Mount (now Lake) Toba in Sumatra, Indonesia. the Toba event is well chronicled geologically as a layer of volcanic ash (or tuff) can be correlated across much of Asia. The ash cloud would have caused a localized winter and guess where! Prevailing winds would have carried the ash cloud around the globe and East Africa, birthplace of Homo sapiens, is at the same latitude.
The near extinction of our species was almost certainly true but what happened was truly marvelous. A mass exodus lead to the classic survival of the fittest and perhaps those 2,000 survivors carried the "right stuff" to evolve into the intelligent life form called "humankind".