He contends that there likely isn't a sentient civilization within about a billion light years of us because the signature of Dyson spheres would be unmistabkable and unmissable. Now this isn't to say there isn't one that's say, 600 million light years away that built their first Dyson sphere 500 million years ago although, in practice, this doesn't really change the probabilities that much.
If there's FTL then that billion light year practical limit really goes out the window as you can effectively get anywhere in the universe, making the volume of absence be many, many times the size of the observable universe.
I'm not sure why the author is talking about gravity ripping you apart in a black hole. It Is Known [tm] that larger black holes have pretty gentle event horizons.
I'm not sure why it matters that a black hole would be spinning. You can pretty much assume every significant mass in the universe is spinning to some degree (a state of zero spin being highly unlikely over even small amounts of time).
The author talks about the inner event horizon and I guess that's the point. But all of that is highly theoretical. Nothing is known about the inner workings of a black hole. It's all highly theoretical and beyond the ability of general relativity to describe. No other theory has been able to adequately explain or describe gravity let alone extreme gravity so your view on what's within the event horizon probably depends on which unproven theory (eg string theory) you subscribe to.
So this is speculation based on speculation.