Read the article? Your questions are answered there.

I just assume ssn is for a us audience and its worlwide with equivalent numbers but who knows. I mean there are only 8 bil on the planet so thats like everyone except maybe china, india, and africa

When applying to a US government position with a certain security clearance, they will do background checks of you, your family and extended family, if need be.

And I’m sure that can be the case for any employer who needs background checks. That being said, I also suspect some of these people in the database are dead.