I haven't been able to make heads nor tales of his logic. In Guangdong province, at the peak of the outbreak, 0.47% of people tested were positive. Guangdong province has a population of about 110 million people. If that was a representative random sample, that would mean a lot of infections, so he's clearly relying on the fact that it's a sample of people who saw a doctor because they had symptoms. Except that I don't see how you can use that to say anything about asymptomatic cases. It just doesn't make sense.