I agree. Probably Toba. I've seen estimates as low as 2,000 for the worldwide human population after Toba. Most are closer to 5,000 with some ranging up to 10,000. Even so, not many people for the whole world.
The Last Glacial Maximum(LGM) 18-23,000 years ago thinned out the human population dramatically too.
Why??
I'da moved South!!!