Perhaps because the article is about how Rust isn't the magic bullet to everything, and a few people have commented agreeing with the article, others feel more willing to comment their own Rust isn't perfect opinion as well.

If you go into the comment section of a pro-Rust article, where the first few top-level comments are also pro-Rust, the responses to people expressing a negative attitude about Rust tend to (in my experience) be different.

This phenomenon certainly isn't exclusive to Rust (or HN). It happens all the time, especially when a prolific commenter is among the first few comments. It can set the tone for the entire comment section.