After numerous leaks, Facebook's internal security team became very good at identifying leakers. The person responsible for this 2016 post was identified within hours and terminated the next day: https://www.buzzfeednews.com/article/blakemontgomery/mark-zu.... The leaker was easily identified by the names of friends liking the post (that and part of their name was visible).
Facebook-issued laptops are filled with spyware, monitoring everything down to the system call level, and practically every access to internal systems is logged at a fine level. The only way to exfiltrate data with plausible deniability would be to photograph the screen with an individually owned device. The fact that you searched for the internal wiki page and viewed it are nothing, but that you shortly invoked the keyboard shortcut for a screen capture, then inserted a USB drive, and copied a file ("Screen shot ____.png" even!) to it (all logged) ... congratulations, you're caught.