This isn't a road rage incident like the news says, It's their son-in-law.

The parents got the shot and did not inform the daughter of it.

Due to a condition with the grand child, the family was exempted but the grandparents got the shot and kept it secret. The grand child's symptoms grew so bad that she passed and it was found that it was due to "shedding".
Hence, he's loosing it on the parents for lying to the family and causing the death.