You might have a point there, except what what would stop them from sending Meg or a cohort to kill any remaining family members.
I think the wounds to the mother's (and Jess') body seem to specific (very caesarian) to be an accident. Could fit though, we know next to nothing and the characters don't like explaining anything to each other.

I was so worried that they would use the actor who plays Papa Winchester to play The Demon again, I think he played the demon in the pilot to stay with a body type or something. That would have been trauma inducing!