You’re correct, the HR dept is there to protect the company. And the actions of the employee sending gore vids potentially harms the company. Thus, HR will protect the employee when it protects itself. Think how HR would step in if someone was sending porn. That would harm the company. HR would intervene.
They only don’t do shit when they can get away with it. Anything that a court would find absolutely objectionable (not maybe) will be curtailed.