It sounds about right.
The key points in the article are
"Last week, Caixin published the results of a seroepidemiological study carried out in April on 11,000 Wuhan residents, which found that five to six percent of those tested had antibodies for COVID-19. If extrapolated to the city's entire population, this would mean approximately 500,000 of the city's residents have been infected with the disease.
Given that the Chinese government has only reported 50,000 cases in Wuhan, it would mean that 90 percent of cases have not been detected. "
So 5% or 6% might have been infected and that is a lot more than the reported figures.
Something similar is probably be true everywhere that has the virus and as antibody testing becomes more widespread, we will get similar stories from other countries.
The only news here is China manipulates the news which is barely news.
The 5% or 6% number is interesting but from my perspective is disappointingly low. The more people with antibodies the better. I hope our under reporting of cases turns out to be much higher once we get the numbers from our antibody testing.