I closed that thread, the maturity level in there is... highly variable. There's a lot of kneejerk statements in there.
Meanwhile, this decision was made or led by one of the few people that developed multiple popular programming languages. I trust his opinion / decision more than internet commenters, including my own.
I am not sure if we see the same thread. There is one reaction from "Rust" dev (who seems have a very new account on github) on why not rust. Most of the others seem to be from C# side.
The pattern also seems to be the same on reddit thread. There is one post about why not rust, equally (or more depending how you weigh) is how other people react to this news.
What is weird is how much people talk about how other people react. Modern social media is weird
There's at least 3 top-level threads criticizing the decision not to rewrite in Rust. Including a RIR banner ad posted in the replies.
Holy Language Wars are a spectator sport as old as the internet itself. It's normal to comment on one side fighting another. What's weird is pretending not to see the fighting
I do like seeing there's threads (on here and in the github page) advocating for or asking about C#, it's healthy to bring up different languages.
But, advocates for language X need to make sure they read and understand the requirements and tradeoffs, which could probably have been communicated better.
Edit: I have reached the bottom of the thread and still have not seen this visceral reaction mentioned by the OP.