Sun Roof problems of the 2007 Chevrolet Impala

2007 Chevrolet Impala ltz 17k I was driving down the highway at 65 mph. I was about to exit and I heard a loud pop and glass fell all over me. I looked and saw about a 2 foot hole in my sunroof (the shade was open). I pulled off the road and called the police. I was not near an overpass, it was night, no cars were around. I did not find an object around the car or in the car. The florida highway patrol determined that it was not an assault (something was not thrown at the car). I called gm and they referred me to my dealer. I dropped the car off today but the service manager was very doubtful it would be covered. He kept insisting it was a rock. The strange signs though are that my sunroof exploded outward. The glass is clear bubbled outward and the shards stick up out of the car. I took pictures of this. I researched this and found that this has happened to many (although not my vehicle) before. The service manager said they would find the impact point and show me when they did (he actually assumed it was a rock before even looking) but he could not explain the outward glass pattern (except to say crazy things happen with glass). He later admitted that he had seen this before but never on an Impala only on a corvette and that was a defect. He said if this was a defect it would have been reported. I told him I was going to report this to the NHTSA but he told me that gm would do that. At this point they are investigating although he said he was very doubtful that anyone from gm would come out and that I would probably have to go through my insurance. He said it is covered in florida with no deductible. Looked into that and it is not true, sunroofs are not covered. This is clearly a defect. This car is only a year old. The violent way this shattered with no one around and the actual bowing out of the glass and all the glass on the outside of the car is pretty strong proof. I had a few cuts, but had I not been more alert this could have been a major accident.