The following is taken from a website:
Sir, do you realize your wife fell out of the car several miles back?
The expression fell out here, as I checked in the dictionary, doesn't make any sense.
Does it mean fell off?
You have laid the stress on the wrong phrase thereby getting distracted. Look now:
"Sir, do you realize your wife fell out of the car several miles back?"
out of = off
You get in a car and so you get/fall out.
You get on a bus and so you get/fall off.
I have heard that the reason behind this is that you step down into cars while you step up onto buses.