I'm a software engineer at Facebook working on security and privacy. This is simply a hoax. The html source shown in the video clearly says "No test user was deleted". We've verified in our logs that the victim account was manually deactivated by visiting
https://www.facebook.com/deactivate.php. Anyone can visit
https://www.facebook.com/whitehat/accounts/ and verify that the query parameter used by this endpoint is selected_test_users not selected_users. We've also audited our code to verify that there's no variant of this exploit that works against that endpoint or any other that we've found. In fact, the most recent code change to this endpoint was in April and was routine maintenance that had no security implications.