There's a lot of shit that has become "best practice" over the last 15 years, and a lot more that was "best practice" but fell out of favor because reasons. All of it exists on a continuum of what is actually reasonable given the circumstances. Reviewing pull requests is one of those things that is reasonable af in theory, produces mediocre results in practice, and is frequently nothing more than bureaucratic overhead. Consider a case where an individual adds a new feature to an existing codebase. Given they are almost certainly the only one who has spent significant time researching the particulars of the feature set in question, and are the only individual with any experience at all with the new code, having another developer review it means you've got inexperienced, low-info eyes examining something they do not fully understand, and will have to take some amount of time to come up to speed on. Sure they'll catch obvious errors, but so would a decent test suite.
Am I arguing in favor of egalitarian commit food fights with no adults in the room? Absolutely not. But demanding literally every change go through a formal review process before getting committed, like any other coding dogma, has a tendency to generate at least as much bullshit as it catches, just a different flavor.
Code review is actually one of the few practices for which research does exist[0] which points in the direction of it being generally good at reducing defects.
Additionally, in the example you share, where only one person knows the context of the change, code review is an excellent tool for knowledge sharing.
[0]: https://dl.acm.org/doi/10.1145/2597073.2597076, for example
Oh I have no doubt it's an excellent tool for knowledge sharing. So are mailing lists (nobody reads email) and internal wikis (evergreen fist fight to get someone, anyone, to update). Despite best intentions knowledge sharing regimes are little more than well-intentioned pestering with irrelevant information that is absolutely purged from headspace during any number of daily/weekly/quarterly context switches. As I said, mediocre results.
You're free to believe whatever you want, but again, this is one of the few things that we actually empirically know to be working.
And there is worst: in the cases when the reviewer has actually some knowledge of the problem at hand, she might say "oh you did all this to add that feature? But it's actually already there. You just had to include that file and call function xyz". Or "oh but two months ago that very same topic was discussed and it was decided that it would make more sense to wait for module xyz to be refactored in order to make it easier ", etc.