Handling negative feedback on a PR is a necessary skill for a developer. A manager should only get involved if it becomes hostile. Negative is very far from hostile.
If they are going to their manager, and then the manager, rather than convincing them that they are over-reacting, is instead going to you and telling you that there's something wrong with the feedback you gave, you should handle that negative feedback.
You’re overlooking the fact that your threshold for what a “conflict” is might be different from the next person’s.
There’s no universally “correct” way to label whether something is a conflict or not. People have varying perceptions.
No one is saying that the boss should be looking for and trying to mediate "conflicts" no one wants them to resolve.
I think the original comment said something to the effect of “employees shouldn’t ever resolve their own conflict, their boss should do it for them”.
I was only trying to illustrate that there are some people out there who are incredibly sensitive and will make a conflict out of the color shoes you’re wearing. Sometimes it’s good to empower an employee to speak their mind about their coworkers hideous color shoes, no need to force boss man to relay the message.