From the arXiv blog:
My objections to this proposed 'solution':“Assuming the average communicating civilization has a lifetime of 1,000 years, ten times longer than Earth has been broadcasting, and has a signal horizon of 1,000 light-years, you need a minimum of over 300 communicating civilization in the galactic neighborhood to reach a minimum density.”
a) What is the rationale behind a civilization lifetime of only 1,000 years [Civilization on Earth has been around for more than 4,000 years]. They´re possibly assuming that a technological civilization will somehow kill itself. But that argument is only a conjecture.
b) Why would a tech civilization be unable to send a detectable signal to over 1,000 light-years? If they are deliberatley trying to establish contact then they could/would make it sure that the signal would be strong enough to be detectable at greater distances.
c) Why they would limit themselves to EM radiation?