I don't think they realize this is the reason many people don't get their news from main stream media anymore. Because you can just read the source's blog and twitter feed.
So in this case a journo is frustrated that a source who they should have been able to echo, and call that news, has their own agenda.
There is zero evidence of this within the leak.
I mean: We're still dealing with climate change denialism after years of the media allowing false equivalence to obscure the overwhelming scientific consensus around it. Major news organizations will run headlines based straight off the contents of tweets by wikileaks inspite of their repeated false claims in the past like with the "leaks" post-coup in Turkey, or Assange's statements about the Panama papers
It's stuff like this that give me, someone who believes fake news are just articles about things that didn't happen published by news organizations that don't exist on social media, major trust issues with American media today (and don't even get me started on British media)
Grouping all "media" together isn't meaningful; it's like saying "all programmers are lazy". It doesn't provide information that helps identify and solve a problem.
Some specific news outlets, especially Fox and the WSJ, actively promote climate denial.
Yes, mainstream media has gotten better about that topic in particular, but in general journalists still go for the easier "stories" that can be portrayed as competing sides, or simple narratives in general rather than what would actually inform people about the world.
Journalists, AFAIK, are supposed to avoid inserting their own judgement, give the reader the information (including opinions of different sides), and let the reader make their own decisions.
We can say that journalists should present "facts", but who says what the facts are? In the end, it comes down to expressed judgments by humans.
That being said, that can be taken to too much of an extreme, as it has been with climate change. I don't need opposing opinions about whether the Sun will rise tomorrow.