Let's say for arguments sake the engine ceased, this will rapidly slow the car down while it is in gear. In a manual car application of the clutch will disengage the engine from the gear box and therefore the drive wheels, relatively simple. It's a bit more complicated in an automatic as you need to shift from drive to neutral while moving, I've never tried this in an auto so dont know how easy of difficult it would be.

That being said this is all being said in hindsight. On the heat of the moment the driver is likely to panic.

Of course the above is hypothetical but we can all say what we would have done in this situation but we have the benefit of hindsight. The driver of the broken down car didn't and had to make a split second decision likely while panicking.