To understand much of our language, Gnorts would have to already be aware that our words and symbols gain meaning from how they're used, and you couldn't, for instance, determine that a swastika is offensive (in the west) by its shape alone.
In this case, the term "colored people" gained racist connotations from its history of being used for discrimination and segregation - and avoiding it for that reason is the primary principle at play. There's also the secondary/less universal principle of preferring "person-first language".
There are numerous changes over the first two days, Exercise to the reader to find which HN comments inspired them.
To note: I really have no problem with him updating his piece to reflect accurate criticism, I do find issue with doing it silently, and with not reflecting on how it should influence his thoroughness in the future.