re: We work from what we know to what we can imagine (unless we are writing SF).
Evolution gave us winds and legs I could imagine your life forms existing and have time to time played devils advocate for multi celled life there, but I prefer to fence sit (after all I'm no biologist).
Neither were the authors of this paper judging from their listed affiliations. The idea that Mars had abundant water early in its history but has been cold and dry for the latest period of its history, the Amazonian, was already the accepted theory.
The authors of the paper presented nothing to conflict with idea that there could be localized releases of subsurface water even up to the current time. Microbes could have been carried to the surface by such water or have been revived by this water on the surface.
- Bob Clark