How? Presumably tens of thousands of employees read it; how can you possibly know which needle in that haystack converted it to a different format and then sent it to a reporter? Especially if it was done over Tor or similar? How exactly do you track that? There are technologies that work that allow for anonymous means of communication.

Is there some positive net benefit of Google releasing the details of the person they fired for leaking the internal information? Companies rarely mention details about firing employees for misconduct.

Well, they didn't and it resulted in a war of leaks. Now anyone with inside information knows they can settle scores by doing it. I think we will see a lot more of it. Good for justice, not so good for Google...