2 billion accounts, not users.
My wife, for example, created 5 accounts. None are actually used for anything anymore. In fact, she can't remember the last time she accessed FB ... probably seven or eight years ago. I'm absolutely certain that she's not the only person on the planet with multiple orphaned accounts.
So that 2 billion is nowhere near near 2 billion actual people, and Zmuck knows it. Don't you just hate the way marketards corrupt everything they touch?