In addition to those with specific antibodies to COVID-19 (which shows up on a PCR test), some number of others probably have cross immunity from exposure to other corona viruses (which doesn’t show up on the test).
Cross immunity might be the reason that so many are asymptomatic. It could be pretty widespread.
Let’s get the science correct. Antibodies do not show up on PCR
If cross immunity exists, then if one were to give someone a cold, then they would have immunity to the wuhanvirus as well.