From that link you provided , I suspected you were wrong and you are wrong about test results after being vaccinated since a vaccination can produce antigens. A vaccination might produce a false positive on an Antigen test, which is the one US citizens need:
After getting a COVID-19 vaccine, will I test positive for COVID-19 on a viral test?
No. Neither the recently authorized and recommended vaccines nor the other COVID-19 vaccines currently in clinical trials in the United States can cause you to test positive on
viral tests, which are used to see if you have a
current infection.
If your body develops an immune response—the goal of vaccination—there is a possibility you may test positive on some antibody tests. Antibody tests indicate you had a previous infection and that you may have some level of protection against the virus. Experts are currently looking at how COVID-19 vaccination may affect antibody testing result