"It's impossible to earn a billion" means it's impossible to work hard enough to deserve to have a billion dollars in a world where so many people died for lack of money, not that it's impossible to get it without cheating.

Another solid interpretation is that nobody gets a billion in wages. You have to own something that appreciates, and it appreciates because of the people who work for you, and you take disproportionately much of the benefit.

How does it work with theoretical distant poor aliens and any amount of money?