I don't think you were wrong to describe him as horrible. He was horrible. Does not mean you think he is entirely responsible at the age of 4 for being like he is.
And I do think horrivble behaviuour at this age should be taken more seriously than it currently is. Putting it down to 'oh he can't help it' 'he has a rough time at home' 'he is just spirited'. If they are horrible it needs addressing, whatever the cause for the behaviour.
And i'm sorry but some kids are simply horrible. Perhaps an unfortunate combination of homelife and genetics, who knows. I remember as a child a boy in my class was just that. I remember thinking as a child he was just pure evil, some of the stuff he did to other children. Seemed to have a nice house, family and siblings who were certainly not horrible, but as a kid myself, who knows.
At age 7 he deliberately killed his neighbours puppy. A fucking puppy for gods sake. We know this because the neighbour was also a child in our class and her father had caught him doing it.
He later went on to murder his girlfriend when he was 17.
Since this, I do unfortunately believe there is a minority of people who are just simply born evil.
Not saying this child is anywhere near this extreme. But not being allowed to say he is horrible, when he clearly is being, is just nuts.