The team’s non-detection of any obvious alien-filled galaxies is an interesting and new scientific result. “Our results mean that, out of the 100,000 galaxies that WISE could see in sufficient detail, none of them is widely populated by an alien civilization using most of the starlight in its galaxy for its own purposes. That’s interesting because these galaxies are billions of years old, which should have been plenty of time for them to have been filled with alien civilizations, if they exist. Either they don’t exist, or they don’t yet use enough energy for us to recognize them,” Wright said.
Two things leap to mind, the first being that our own universe wouldn’t pass this test. We’re advanced enough — and curious enough — to have an inkling about how to go about looking for space pals… but we don’t leave much of a footprint.
The second item is brought up almost immediately in the comments: the tools employed by a somewhat sophisticated civilization might be “noisy” as far as radiation goes. But with greater advancement comes greater efficiency, with cooly-operating components, and narrow-band, point-to-point communication that may not be picked up from the outside.
So, to the above I say that we need to keep looking.