Apparently the Facebook story is not the content that was intended to be shared, but rather a story linked in a tweet that is linked in the tweet that was shared, below the Facebook story that was linked:
This appears to be an article from 1999, and does not talk about the more recent migrations between instruction sets.
Cases like this suggest that a serious portion of the HN users just upvote posts based on the title without ever opening them. The current title is very misleading.