It does sound suspiciously like wishful thinking though, doesn’t it? You can’t sample all parts and all fluids of someone’s body all the time. Maybe trace undetectable levels of the virus can be transmitted, and of course they are going to look like a “no transmission” case if you lack the ability to detect that amount of virus. And that’s either not a problem (if trace levels = no symptoms), or a ticking time bomb waiting to find a host with the conditions that would enable mass viral replication back up to detectable levels.