Ah, I see. I actually originally posted the x.com links but plenty of HN users can't read Twitter threads that way, so we usually try to provide a readable alternative. (Plus this helps to reduce offtopic complaints in threads.) You'll therefore often see both a twitter/x link and the corresponding xcancel link in toptext - like in these recent examples:
In the current case, I decided not to do that because it would have made the toptext way too noisy, so I chose the domain that most people would be able to read.
As for HN's policy, you're right about the rule but not its scope. It only applies to submission links, i.e. the URL that a story title is linked to, which also determines the domain displayed to the right of the title.
This doesn’t seem correct. I can view all of these without a Twitter login. Compare this with nytimes, where a login is required but we still always post the canonical URL per the guideline.
> Plus this helps to reduce offtopic complaints in threads.