This is just incorrect. The NHTSA recommends to stay in normal riding position in the vehicle if you need to stop your car on the highway. Yes, you can still get hurt in some circumstances but your neighbor could be dead instead.
I think he meant you shouldn't stop in the fast lanes to begin with. Clearly if you have stopped and cannot go then stay in the car with all of its safety gear and crumple zones, but don't stop if you don't have to.