That study is an extremely weak support to the claim that this virus can't spread asymptomatically - it's nearly useless for that purpose. They only studied a small number of people at the very tail end of the infection who showed that they had some evidence of virus in them. They did not look at whether those patients actually had an active infection - they could have simply been detecting remnants of dead virus in their systems. They certainly didn't look at all at people in the incubation stage pre-symptoms.