Actually, I think they found the bottleneck in the DNA and then went searching for a cause...and, found Toba.(Not positive though)
I think the DNA bottleneck is still there.
The Chinese Homo Sapiens died out at the bottleneck and re- radiated back to China while the Hobbits survived in place? I’m assuming that the current day Chinese are genetically related to the rest of mankind and the bottleneck survivors. The Chinese could be mistaken too.