"No alien civilizations have substantially colonized our solar system or systems nearby. Thus among the billion trillion stars in our past universe, none has reached the level of technology and growth that we may soon reach."
While the article is in a way all about exploring that disconnect, it's a bit strange to find it written down so explicitly in the conclusion. We can ascribe a very high level of confidence to hypothesis that neither our own nor any of the directly neighboring star systems have been colonized. But to postulate that therefore the universe has not yet produced a civilization as technologically sophisticated as our own is still a non-sequitur, at least in my opinion. The article also makes a lot of assumptions (it has to!), some plausible, some seemingly arbitrary, which might in the end not be important factors at all. For example, any consideration about radio communication must be on very shaky grounds, in particular when charting the absence of it.
The reason why we're not seeing alien neighbors or predecessors (which would be "neighbors" in time), might well be a combination of factors. While we can exclude certain scenarios, such as a cloud of Von Neuman Probes eating the galaxy, it still leaves room for a lot of little factors that can change the galactic stage for us in a fundamental way - especially if they work in conjunction.
For example, the average duration of the technologically recognizable phase a civilization goes through may be smaller, and there may well be less of them than expected. In addition, willful avoidance or isolation may well play a role; the zoo hypothesis is an extreme example of this, but in a sparse cosmos the measures you have to undertake in order to isolate an emerging civilizations become less heroic.
It's also worth mentioning that we ourselves are not past the Filter by any means. In fact, as time progresses, it seems to become less likely we'll ever move off the Earth as an exclusive habitat. Part of this is due to psychology, we could have made it happen by now but didn't. The best bet at becoming an interstellar civilization right now seems to be to wait until we're pure computer systems, unburdened by aging and the passage of time, but that development, too, might end up being something we never elect to actually pursue.
Luckily, this whole thing is a mystery we can solve over time, just by gathering data about what's out there.