The eruption of Mount Toba is indeed a mystery and continued to excavated scientifically. The Toba eruption indeed entirely undocumented in the book, but the scientific evidence in the present.
It is estimated, about 73,000 years ago Mount Toba erupted and nearly destroyed almost all living creatures on Earth.
The explosion of Mount Toba Supervolcano which is referred to as the greatest boom in history of the volcano. The explosion unleashed the 2,800 cubic kilometres of ash that spread and envelop the Earth's atmosphere for six years.