That's assuming the exact opposite of this paper; that there's _infinite_ other civilisations, which is as obviously untrue as the idea that there are none.
If the period of time before all high-power communication is encrypted is short, then the likelihood that the period of our ability to pick up unencrypted high-power communications will intersect it is potentially very low.
The universe is _huge_. Most of our communications will not be audible above background radiation after a little way out - this could be no different for any other civilisation's communication technology. You don't use a nuclear reactor to power a cell tower, and if you don't put that much power into it then it's not gonna be detectable ten light years out.
If the period of time before all high-power communication is encrypted is short, then the likelihood that the period of our ability to pick up unencrypted high-power communications will intersect it is potentially very low.
The universe is _huge_. Most of our communications will not be audible above background radiation after a little way out - this could be no different for any other civilisation's communication technology. You don't use a nuclear reactor to power a cell tower, and if you don't put that much power into it then it's not gonna be detectable ten light years out.