Finding viral RNA does not mean that it comes from active virus that can still infect people. It can be just dried out inactivated virus.
>we could not conclude that the viral samples in this collection retained infective ability
Yes that's a big limitation of the sampling/testing done. However, and here I'm editorializing, they found viral RNA everywhere.
While the following discussion might seem obvious to epidemiologists, I'm a lay person and it wasn't obvious to me:
Several aspects during the COVID-19 pandemic support the risk of aerosol transmission of SARS-CoV-2. First, mounting evidence for pre- and asymptomatic transmission, where the spread of droplets through coughing and sneezing cannot be a major factor, must raise questions about aerosol transmission. Second, aerosols generated by speech could theoretically contain enough SARS-CoV-2 virus particles to support transmission, and these aerosols can remain airborne for up to ten minutes. In addition, coronaviruses can be emitted in aerosols through normal breathing. Third, field studies in hospital wards have detected SARS-CoV-2 RNA both in vent openings and in the air. These findings are not unexpected seeing as similar observations have been made for both SARS and Middle East Respiratory Syndrome (MERS).
That supports the idea of aerosol transmission. I don't plan on spending a lot of time indoors, other than in my house, this winter.