Is the person who quarreled with the deceased driver sinful for the car accident that occurred because the driver was upset by his words, or is the driver solely responsible?

The ruling concerning the deceased driver is difficult due to the lack of details about the accident and his level of awareness while driving.

The second person bears no responsibility for this, as long as he was absent from the accident.

It is advisable to refer the matter to the Sharia courts for consideration. And Allah knows best.