Are We Living Inside A Black Hole?

"When the density of matter reaches gargantuan proportions (more than about 1,050 kilograms per cubic meter)"

I assume there is an a missing exponential in there (10^50?), since lead is an order of magnitude more dense than 1050 kg/m^3

Kind of nitpicking, but with an error like this I have to wonder about how well any of this is actually being explained. (Actually, given the accuracy rate of news articles on a science topic I'm very familiar with, I think I know the answer, unfortunately).

Seeing as Einstein's theories are based on math + the observable universe (and that they explain events as we see them in our universe), how can we say that our universe is governed by a specific part of Einstein's theory, namely the behavior of spacetime inside of black holes?

Seems fairly circular to me.