The shift **** has a lock on it. If it isn't locked into place it can come off. Looks like it wasn't inspected before you got the car. Talk to the service department. I'm sure they will take care of you. The **** is part of the car prep before giving it to the new buyer.

However, hitting a vehicle in result of it is kind of your own fault. Just because a **** comes off, does't mean you lost all control of the vehicle. It just in reverse gear! Your brakes, steering wheel, and clutch pedal were still fully functional right?

I know if I had put it in reverse and it came off, I just wouldn't let off the clutch.