The danger factor of a 8 month old differs greatly depending on how they are handled.
Also could be the "owner" of the colt is lying because colt is older too.
If colt would not quit chasing, pretty easy to have this happen, and have seen some horses so absolutely aggressive that they will not get settled down period.
Youngest horse I know that did breed mare, was 12 months old. He was papered so knew how old he was.
Something clearly happened, and a horse is dead.
Horses make me a better person.