This is the interesting part of the article:
But "swabs taken from the air exhaust outlets tested positive, suggesting that small virus-laden droplets may be displaced by airflows and deposited on equipment such as vents".
Which is a direct quote from the abstract of the study.
The exhaust they're most likely referring to is the ...
This is a rather tentative answer since the evidence still looks fairly contradictory to me, but the BBC has an article that reiterates what DW says, with more detail:
Thanks to the laws of thermodynamics, cold air can carry less water vapour before it reaches the “dew point” and falls as rain. So while the weather outside may seem wetter, the air itself ...