I'm glad your parents are safe but the design of their car was not what kept it from catching fire, it was more likely the fact that it was diesel. You can put a match to diesel fuel and it won't catch fire; it take a lot of heat and pressure to combust diesel.

And electric cars have better and larger crumple zones making front impacts more survivable. This is due to them not having an inflexible engine taking up most room in the front.

Which kind of accident is more common? Bottom impacts or front impacts?

Are you sure you have the speed correct? The approximate top speed of a swift is 170km/h. I find it very hard to believe that the car managed to speed up further to overtake, and subsequently crash without any injury to the occupants.