This is an interesting idea with a lot of merit. It centers around the idea of panspermia. That is, rocks and dust ejected from planets in asteroid impacts could carry the spores of simple life to other planets, perhaps even in other solar systems.
These life forms may not have the biochemistry we expect. We think of oxygen atmospheres as a reliable biosignature, but there may be thriving life that doesn't produce or need that.
But they would have "something" in common, and it would be clustered around the orbits and dispersal of the ejecta that colonized these different worlds via panspermia. What this proposal is suggesting is to look for clusters of exoplanets with any common characteristics in these dispersal patterns, and zero in on them for closer examination.