"The couple were together for 14 years and raised Vinson and his 15-year-old brother, Kyle."
The word "raised" can mean a lot of things to a lot of people, one man's tossing a ball, teaching to fish etc. is another's physical and/or verbal abuse, resentment and emotional neglect. If you're stabbing your StepDad "7-9 times" either you're mentally ill or something outside the scope of normal in terms of parental/child dynamics was going on. Violence begets violence, there's more to this.
"After a few threats, the two allegedly agreed to a fist fight. That Friday, Celena asked the men to talk out their issues but her son refused to. The teen then baited his stepfather into hitting him."
The chances that the kind of man that would allow a young kid to push his buttons to that extent was an emotionally evolved/ mature person by any standard is pretty much nil. Again there's more to this.
Vinson told police he killed his stepfather because he “wanted to throw him out of the house.”
Playing violent video games and watching MMA doesn't create monsters like this - either the kid's insane and they should have seen it coming, or there was some abuse of some sort that's not mentioned in the article.