They tested in hospital/ICU areas. I think the odds are much higher in such an environment. Obviously medical workers should keep from transferring viral material to their homes, but to imply that this is being transferred by non-medical personnel is inaccurate.
Definitely there is more of the virus in hospitals and in the ICU. The virus is also probably on the floors of subway cars, elevators, and other public places if someone infected emits droplets in those areas.
Of course, I'm only suggesting that the idea of shoes as vectors might be something.
