yep! its rust. I wouldn't touch untill your ready. once you open it, up you are going to be sick. look inside the trunk underneath and get some rust converter like POR 15. it will stop it untill you can clean it out . they all rust in rear filler panel and front windshield. the body person did not prep the car with metal conditioner before primer but even so the rust was underneath so it wouldn't help anyhow. good luck and don't freak out. its nothing money can't fix.
