It might not be a perfect cloaking device, but if it can reduce visibility to that one galaxy a few dozen megaparsecs away, perhaps itβs enough to evade the survey that the article covers?
The PDF says they used the data from the WISE all-sky infrared survey to find the 100,000 galaxies, of which a "significant population" had a redshift z of over 2. https://arxiv.org/pdf/1504.03418.pdf
Depending on the Hubble constant, a z of 2 is more than 8000 mpc, 27 billion light years. That's a big search volume, and they didn't find anything obviously artificial.
Due to the finite speed of light, for many of those galaxies the images are a snapshot of several billion years ago. So we have no idea of what is thriving there today.
Okay, but that makes it worse. You can spend a million years beaming your waste heat at an apparently-dead galaxy, only to have one of its indigenous species bootstrap up a technological civilization in a blink of an eye (a mere thousand years) and launch an invasion fleet.
If it's the Dark Forest scenario then it's simply not safe to show any technosignatures at all, ruling out megastructures entirely.
