It's discussed in the link, and elsewhere [1]. Some mod actions on HN are transparent, some are not. You should not assume that, just because you see marks of some form of moderation, that you can see them all.
Undisclosed content moderation is like directly modifying your production database. It's faster, but always more troublesome. Nobody else knows what changed or why, etc.
[1] >>36435312
[1] https://www.supremecourt.gov/docket/docketfiles/html/public/...
[2] https://www.supremecourt.gov/docket/docketfiles/html/public/...
[3] https://www.supremecourt.gov/docket/docketfiles/html/public/...