This is normal. It was going after you not your motorcycle, you must have moved in it swooped past you. If you're on your motorcycle and you hit something that stops you, they will attack. If you have a train of them behind you and you log off, they will attack you as you're logging back on and kill you. There's a period of time when you're not quite in the world and not quite outside of it and they're able to do you damage but you're not able to do anything about it.