Indeed, as TFA notes, there is "something wrong with our thinking", or at least with that of the author.
First, interstellar colonization? Unlikely. It makes nice SF, but there's no good economic basis for it. A civilization that survives long enough to reach the technological level necessary for interstellar spaceflight will have stabilized its population and learned how to use local resources to make their home world a paradise. Why go anywhere else? The expense is enormous, the payoff non-existent. (They're working on stellar engineering, of course, so there's no worry about their sun going nova.) Childish species who still imagine faster-than-light loopholes might dream of going swashbuckling across the galaxy, but grown-up races are content to follow more mature pursuits. TFA's claims about "intelligent life's ability to overcome scarcity, and its tendency to colonize new habitats" are simply handwaving, generalizing from one species of half-bright monkeys into sweeping statements about all intelligent life.
Second, there's the question of signal detection. Contrary to popular belief, radio and TV transmissions probably couldn't be detected at interstellar ranges. We've only sent a handful of signals into space that are detectable at long ranges - and mostly that's content-free radar signals. Why do we assume others are more chatty than we are? I imagine a galaxy full of listeners, each waiting for someone else to start talking. Additionally, compression and encryption make signal indistinguishable from noise.
Third, recognition of "mega-engineering". TFA claims "we see no signs of their activities in space". How would we know? We assume a "natural" explanation for phenomena - as we should - but if we assume the existence of greatly advanced tech, who knows what we think of as "natural" and take for granted out there that's actually engineered?