Hi there! Based on my understanding your thinking is correct. Having a minivan/larger sedan doesn't guarantee you won't get into an accident, just like having a sportscar doesn't guarantee you will get into an accident so there's no sufficient necessary.

If it were a sufficient necessary it would be stated like this: If one drives a sports car, one will get into an accident. My friend got into an accident. So, my friend drives a sports car.

Meaning if one thing happens then this must be true. I hope that helps!