First aid rules of an injury - apply cold or ice to minimise bruising.I have no idea how long it takes for bruises to come out - his hand was bruised. Was it his hand that took the force from and smashed the taillight? Or maybe she clipped his knee like she said and he span round and fell and hit his head on the hydrant?
He was outside, in a snow blizzard with a rapidly falling temperature. I’m gonna say pretty reasonable that bruises wouldn’t necessarily show as much as they would on a warm body.