Mods frequently rewrite submitted titles, either cos it's not the same title used in the article, or because there's a better wording for the HN crowd ¯\_(ツ)_/¯
It's totally ordinary for a post to go front-page and attract hundreds of comments on the basis of a title that's later deemed too interesting/editorialized/whatever, and you later see some dry uninformative title like "Google account security" or whatever it was occupying a top slot.
I can't say I've noticed it often before for text posts, but I do generally think this pattern of closing the barn door after the horse has bolted is pretty silly in general.
Check dang's (HN mod) comments:
https://news.ycombinator.com/threads?id=dang