Sounds like trouble to me.
“Hey I rewrote what you wrote because it sucked. Got problems with that?”
I suppose the best solution to this problem would be a “late review” asking for an explanation, offering a solution, and hoping it doesn’t just get ignored, which is the easiest thing to do for the author.
Reading it like that is just insecurity speaking. If anyone wants to rewrite my code to be more readable, I'd love for them to tag me in the review and show me how they did it, so I can learn. Assuming good intentions and being open to discussion goes a long way :)
I'll always tag the author for review if I'm rewriting something recent. It's more "Hey, I was too late to mention this in the review, but I think this improvement was worth the time. Let me know what you think in case I missed something important about the original."
That’s generally what I like too, but often in teams my suggestions are either approved with zero comments, ignored or followed by wasteful reviews by people who don’t know the language they use every day, and don’t bother to google their answers.
This happens many times in codebases. People begin to 'own' sections of it and they become very protective of what is going on in their area. They take it very personally if something changes and they were not in on it.
I wouldn't probably make a separate PR for that - just refactor the code next time I need to touch it - and tag the author for review of course.