We (moderators) don't ever delete comments (except in rare cases where a user later asks us to do so for privacy reasons).

The most obvious candidate for what the parent commenter is referring to is this one, which has been flagged/killed: https://news.ycombinator.com/item?id=48275838

People do delete their own comments after they've had a moment to consider what they've written. It's an honorable thing to do, IMO.