I don't think they drew that conclusion as it is probably difficult to say in which phase of the illness people get tested. Some have mild (or no) symptoms and

I don't think they drew that conclusion as it is probably difficult to say in which phase of the illness people get tested. Some have mild (or no) symptoms and probably go through their active 9-day period without getting tested at all. Others can have severe symptoms from an early onset, and probably get tested quite fast (hopefully). Some may get severe symptoms after an incubation period, only to get ill when their active 9-day period was over. It should mean that a 10-day isolation for positive cases, combined with high frequency testing should have a massive impact on the spread of the virus. That the virus can be found in your body much much later, in an "inactive" state should not have much impact on the spread.