This is the question that appears in Slashdot front page if you have selected "Willing to moderate" from your user preferences.

As one signature noted in /., the logic is kind of strange because it's backwards: If you haven't meta moderated, it asks if you have... if you have, it doesn't.

It's just a helpful hint, not intended to confuse. It looks better than "Please meta-moderate these comments". It's used to build community spirit. (yeah, right.)