An author can never be 100% correct on anything. Even writing within my own experience, I cannot possibly write the experience of every white, straight, cis, thirty-something, English-speaking, post-colonial woman. All we can do is try to write something that hopefully isn't a grievous misrepresentation, or unintentionally offensive, or completely cliche. To me, implicit in that
try is that when I mess up (and I
will mess up) I will listen, and try to do better next time. (As
@tebakutis has noted.)
Sometimes people have a lot of anger. Sometimes nothing we could have done would have been good enough. They have that anger for a reason, and we just have to live with that. If we can't handle having hurt people then yes, perhaps we shouldn't write about potentially hurtful things such as systemic oppression. If we're going to write about it, and we don't care if we hurt people, then that's pretty mean and selfish, tbqh.
In this particular instance, the book review was 9000 words long because the reviewer quoted extensively from the book. Now, obviously it's possible to do that selectively and paint a skewed picture. But I also believe that anyone's experience of a piece of media is subjective (not to turn this into the Talent thread v2.0

). The reviewer presented her experience and view of the book. That's the right of any reader.
It's also the right of any reader to choose to read or not read any book for whatever reasons move them. So yes, probably some people chose not to read the book because of the review. (I know I did. Not because of the issues outlined by the reviewer, but because from the excerpts and the book description, it looked boring and cliche.)
The swarming of opinion and action is a separate issue. Online harassment is always horrible. And I absolutely never condone leaving a rating or a review on an unread book. But these are things, I reiterate, that happen on both sides of the political fence. The reviewer was hounded on social media. YA authors of colour face massed and punitive one-star reviews of unpublished books just for being YA authors of colour. (One YA author of colour had her editor contacted with trashtalking about her in an effort to get her book pulled.) That behaviour is the issue. The sharing of a genuine opinion on a book's handling of sensitive content is not the issue.
Just in passing: I don't believe any part of this was backlash against the book's popularity, because from memory the review was written before the book was even published, from reading an ARC. No one knew how popular it would be. To be honest, I'm still not sure how popular it is: I'd forgotten it existed until this article surfaced.