Here are post about it with some discussion/analysis:
tldr: It seems like they used an exploit to obtain admin accounts' cookies (the thing that keeps you logged into your account) to gain control of their accounts and potentially other exploits to deface the actual instances.
She went on to say kill a few minutes into the video so it might just be the start of the video. Could be legit or just what people have been conditioned to do for no reason. I've also seen youtubers specifically say that they can swear after the first 30 or so seconds of a video and not get demonitized.