Is this incident considered accidental killing, necessitating blood money and expiation, and does the driver bear any sin or guilt for it, given that he was not reckless and the deceased appeared suddenly before him?

If you were driving at the permitted speed and could not avoid the man due to the short distance, then you are excused and nothing is upon you. However, if you could have avoided the collision or if you were speeding, then you are liable. Liability here means the obligation of expiation (kaffarah) along with blood money (diyah) if the man dies. The expiation is fully on the driver, even if both parties shared in the error.

Traffic accidents are subject to the rulings of criminal offenses prescribed in Islamic Sharia. The driver is responsible for any harm he inflicts on others unless the accident was caused by an irresistible force, an act of the injured party, or the fault of another. If the driver and the injured party both contributed to causing the harm, then each is responsible for the damage inflicted upon the other.

The expiation for killing is freeing a believing slave; if one cannot find one, then it is fasting for two consecutive months. The fact that the man was alive and well after the accident does not change the ruling if his death was due to the accident, as the consequence of the injury is guaranteed to spread, and this is confirmed by medical examination.