Blindly shooting it down like it wouldn't solve engineering problems is just the other side of the same coin. You haven't really provided any constructive info why it wouldn't be a good fit here.
In this particular case, a company the size of Uber isn't going to reap the benefits of RN the same way a smaller one would, and RN's downsides will be magnified. Further, to fix the issues it has with RN it'll need its engineers to do native work anyway, making the extra abstraction layer something of a distraction that could've been avoided.
The comment I replied to read, "Why didn't they use react native?" As if this would have solved EVERYTHING.
It's just a question, and an interesting one at that. Given they were already prepared to (and did) spend so much time rewriting why not kill two birds with one stone and get cross platform on top of it? There very well may be good reasons to have not used react native. It would be insightful to know what those were or even (to a lesser degree) to speculate.
If they were asking that question having not much experience in React Native, then sure, it's just a question.
If they do have experience in React Native, then this does somewhat imply that the asker is saying React Native would have solved their problems.