The Facebook chief, who stands at 5' 7", sat on a cushion during both days of the proceedings, ostensibly so he can be seen as a bigger version of himself and not like a tween wearing a suit. This naturally blew up all over Twitter, forcing Facebook to clarify that, no, Zuckerberg didn't request a "booster seat" to make him appear taller as he's grilled by a room full of congressional dinosaurs.
In a statement to the New York Post, Facebook wrote that it was "the committee’s standard practice" to offer a cushion to whoever is in the hot seat. Zuckerberg merely obliged the offer, because he likes cushions.
While Facebook provided quick comment, that's not likely to be enough to stop the rampant speculation and, you know, all the memes: