I vouched for your comment. It didn't break the guidelines, and therefore shouldn't have been flagged. In the future, you can always email the mods at hn@ycombinator.com if you were flagged and think you shouldn't have been (or other mod-y stuff). (I am not a mod)

Take a look at the 'new' tab and you'll see a lot of flags that shouldn't be flags. Guessing people are using it as a stronger downvote.