Fast Readers

Okay, you're a ghost on the internet which means you're already a weirdo, and you clearly can't figure out why this is funny. It's dark humor, which means that it takes a tragedy and turns it into a joke, and it's about 9/11, which was a real event where many people died. The joke implies the victims fell down the towers very fast, like they were 'reading' the stories of the building in seconds.