You'll notice a dent in the middle of it - like you'd see in the middle of a fired primer. Because it is a primer; when it lands on the pin at the bottom of the tube, the primer firing starts the initiation of the increment charges that have been left on the bomb, depending on the distance to target and the trajectory that the MFC intends for the mission. The fuse and its safety pin is at the top; I'm not familiar with that mortar round, but I assume it has a safety pin on the fuse.
That bomb in the car has 10 fins. I haven't seen one like that ... presumably the nose is buried in the tire and obscured... However the old 2" mortar bomb had a flat nose and was shipped with a steel safety cap that was unthreaded (which exposed a softer thin brass flat cap) prior to firing ... I wonder if we are seeing a bomb that was designed with a similar flat detonator and someone fired it without removing the steel safety cap.