At worse, is the AI interpretation of the prompt (which I don't believe it's the case). There's a reason why there's a second AI (I believe Azure's Content Filter) that filter and remove the AI message when it mention "rule" or "prompt" in the context of a prompt: Because Microsoft knows it's a valid system prompt.

It is far, far more likely that a human would commit a typo to the code base, than an LLM would misspell a common word.

I think it's fake, pretty sure this wouldn't make it past the review process. Or bing is doomed.

Has Microsoft said it is fake?

Guess we'll know if the typo gets fixed :)