The abstract does a poor job of explaining one of the primary motivations of this research: if Alcubierre drives can exist, and can be built, then it seems likely a sufficiently advanced alien species would have built them. We could therefore find them by detecting the drive failures associated with the hypothetical tech, something which is likely easier than actually building the drives ourselves.
Won't it be funny if it turns out WE'RE the most advanced alien species? Like, we're out here wasting time with SETI and this failed warp drive thing, when we should be concentrating on UNIVERSEDOMINATION!!!
This is an actual proposed solution to the Fermi Paradox. We're still relatively early on a universal scale. It's possible we're just.. first. Or so early that hardly anybody else is out there yet. Could be that a billion years later, advanced life is all over the place.
In your formulation, we would also be the explanation for another species' dark forest hypothesis...
The idea is to assume mediocrity, rather than starting with the assumption that a phenomenon is special, privileged, exceptional, or even superior.[2][3]