I attended a business meeting 12 days ago with 10 other colleagues, and one of them was covid positive. however, nobody in the room for 8 hours with him has tested positive since? how can this be?

Everyone's immune system is different. Infection depends upon the amt, exposure time infectivity co-morbidity, age etc. So getting cocid depends on all that

If the people in the room were vaccinated, they may have escaped infection. Some individuals are genetically resistant to the virus. A person may be Covid positive by nucleic acid test/pcr, due to dead virus in the nose and not be infectious. There may be other explanations as well.