The article is making the (almost explicit) assumption that the "power law" holds for civilization populations.
That seems reasonable to me.
But I think we can also find good arguments that we have more information than simply where each of us as individuals appeared.
For instance, the resources of the universe can easily support quadrillions of us (or individual entities), so if even one civilization is able to extend itself to other solar systems reliably, there must be civilizations with quadrillions or more individuals somewhere.
That would strongly imply that while most individuals are in large civilizations, we have counter evidence that we might still be not in one.
Or the argument could be that the power law doesn't hold due to a strong threshold effect, or some other effect.
For instance of some civilizations become galactic, but most individuals still appear in a great many more civilizations that die out before becoming immune to collective disasters.
That seems reasonable to me.
But I think we can also find good arguments that we have more information than simply where each of us as individuals appeared.
For instance, the resources of the universe can easily support quadrillions of us (or individual entities), so if even one civilization is able to extend itself to other solar systems reliably, there must be civilizations with quadrillions or more individuals somewhere.
That would strongly imply that while most individuals are in large civilizations, we have counter evidence that we might still be not in one.
Or the argument could be that the power law doesn't hold due to a strong threshold effect, or some other effect.
For instance of some civilizations become galactic, but most individuals still appear in a great many more civilizations that die out before becoming immune to collective disasters.
In which case, I really hope we are not typical!