I have seen this before on one i was following ( siver ) - only obvios when the sun catches it just so.
i have noticed mine from a distance looks like that a bit too only in certain lights, but upon close inspection there is fa wrong!!
Think that as is a thin bumper and there is a slight amount of distortion where it mounts, the silver paint greatly exaggerates this small flaw. Mine has never been bumped either - known it from new. I think is just aniother little clio flaw - but hey, you gotta love em!!