Is there any chance that the car was being repositioned to make sure that the wheels missed the hog? i.e. that they were trying to protect it and that’s why they smiled. (Possibly depends on what sort of smile it was). Someone would have to have been particularly unpleasant to have tried to kill the hog, purposely.
If you think the person really was trying to kill the hog purposely, that is illegal. But unless you have details of the number plate of the car or know who it was, there probably isn’t much you can do, in that respect. But if you do you could report the incident to the police or RSPCA.
Fingers crossed that the hog is o.k.