And you are told after a while, that your manager can read you a privileged and confidential document and you’re not supposed to even know who contributed to this document, who wrote this feedback, what process was followed or anything. You write a detailed document discussing whatever pieces of feedback you can find, asking for questions and clarifications, and it is completely ignored.
According to her account, she was not given the feedback when she was told that the paper had to be retracted. After discussion, she was told her manager would read her the feedback without telling her who wrote it or what process was followed.
This is different than a normal peer review process that, anonymous or not, aims to provide feedback to the author so they can incorporate it.
Peer review in Academia is anonymous but has relative guarantees that the reviewer will have sufficient knowledge to judge your paper, won't be an academic rival out to skewer your work, and is generally capable of being a disinterested judge. As many others have pointed out here, Google doesn't do peer review in the academic sense, they do pre-publication review, almost always on short notice, for the purposes of protecting IP, mainly.
So imagine you're called in and told to retract your paper on substantive grounds provided by an anonymous reviewer whose feedback is sufficiently bad for you that you don't get a chance to amend your paper, it's just retracted, full stop. You can't have their written feedback, but after you kick up a fuss, you'll be granted a recitation of the feedback that won't change anything about the fate of your paper.
All this in the context of review that's normally a rubber stamp when trade secrets aren't involved.
Demanding to know who torpedoed your paper in an extraordinary way doesn't seem so unreasonable.