Comprehensive Coverage and Sunroof

Have any of you ever had your sunroof in your car just break , it was basically like it exploded? I bought my wife a car literally less than two weeks ago brand new and she went on a girl's trip this past weekend. Of course all the girls want to take the new car (I told her from the beginning that she should let someone else drive but that's neither here nor there). On their way back the sunroof busted out for lack of a better term.

So I look at my options glass isn't covered under warranty obviously so the only option I have is to put in an insurance claim which is what comprehensive coverage is for or so I thought.

Progressive is now telling me that this might not be covered unless we can tell them how it happened. Obviously I wasn't there so I don't know, but my wife doesn't know either. It could have been a rock I suppose but we can't find any evidence of a rock inside the car which doesn't rule it out.

My main question is is it right for them to deny this claim just because we can't provide or prove causation???? I thought comprehensive covered this type of non-collision damage no matter what as long as it wasn't intentional.