Is what the Companion did considered intentional killing, accidental killing, or divine decree, and what are the legal ramifications of it?

What your friend experienced could be one of two things:

1. If he took safety precautions, did not exceed the speed limit, and was not driving while exhausted or drowsy, then there is nothing upon him if the accident occurred and he was unable to avoid it.

2. If he did not take these precautions, then it is considered accidental killing (qatl khata'), which entails two consequences: expiation (fasting for two consecutive months) and blood money (diyyah) to be paid by his 'aqilah (male relatives on his father's side).