But it could be, and that is what the statute says.
In fact the statute doesn't even suggest, by my reading of proposed paragraph 672.64(1)(b), that you're looking at future behaviour. You're looking at a past incident. At least in proposed paragraph 672.64(1)(a) you are looking at the likelihood that a person would “use violence that could endanger the life or safety of another”. It has “will use violence”.
Here you have a retrospective observation saying “...the offence were of such a brutal nature as to indicate a risk of grave physical or psychological harm to another person”.
You have one incident causing harm.