No, the discussion started with a the article from Bun, stating that rust has some technical advantages for them. The response from the Zig creator is a bunch of personal attacks directed at one guy, like calling him a stinky manager. All of these are fully unrelated to which language is better for Bun.
This is like the textbook definition of an ad hominem.
To be pedantic the ad hominem fallacy is about trying to deny an argument by attacking the author, so in a discussion about zig Vs rust if Andrew isn't trying to enter the discussion and just argue "that guy was stinky, glad he is gone" is not really an ad hominem, just not classy let's say.
> This is like the textbook definition of an ad hominem.
No, it isn't at all. Ad hominem is only in effect and fallacious when the logic turns on the personal attack. "You're wrong because you're stupid" is ad hominem. "You're wrong and also you're stupid" is impolite, but logically fine.
To clarify, I think that the entire "History" section is unrelated to Andrew's argument, only the "Addressing the Blog Post" section actually contains arguments, and that section doesn't contain the rude comments, it's focused on technical decision-making.
Ad Hominem is only a fallacy when the speaker's personal qualities are irrelevant to the topic at hand. When one man has unilateral control over a project, you have to consider it as an extension of their personality.