You know it's a bad car accident when people who weren't even in the car file a personal injury claim with your insurance company. Actually, this is a scam known as "the phantom victim." Whether an after-effect of a staged accident or a cash ploy that comes later, the scammer will attempt to file claims for additional passengers in the car, claiming pain or injury, even if no one else was present. (It's especially easy for scammers to try this with online claim filings.)
Unless you follow around the other driver for weeks, you can't really prevent this scam, but it can be thwarted. When gathering information after an accident, such as the other driver's license number and contact information, also count the number of passengers in the other car (if any) and take photos of the other car, its passengers and the general scene. Report any fishy circumstances to the state insurance fraud bureau.