Is accidental damage covered by warranty?

My 2016 Renault Koleos Intens recently started displaying a sensor problem on the dashboard. We got it checked by a local dealer, not the seller, who told us that one of the front sensors has been damaged by either another car or by kicking by a shoe. There is small dent on one of the front sensors but there is no scratch mark anywhere around it. There has been no accident or hit on the front part either. How did this sensor get damaged? And how it is affecting the rear sensors? Who should cover it? The warranty on it is for five years. I am disappointed with their response.