Please Explain Lane Splitting

A good friend was severely injured lane splitting. He and a friend were in a stop and go situation and going between cars at less that 30MPH. His friend passed a car and immediaely after he went by the car a college kid opened the passenger door to jump out to see what was causing the jam. My buddy couldn't stop. Hopitalized for 6 months. Still has a plate in his head. And, that was with a helmet! He has been riding all kinds of bikes since he was itty bitty. I won't split lanes any more.