No, screaming at someone is not violence. The WHO definition you cite also restricts its definition to physical force. If screaming were violence, we'd have prisons full of sports fans after every football game.
"Harming someone" is anything which causes harm. We have different words to describe different things. In this way, we can tell them apart when communicating with each other.
Not all violence is wrong or illegal, and not all screaming is violence.
Words are defined by people. By seeing violence as a spectrum you can see the spectrum of possible responses to violence. We can then distinguish the different forms of violence with other words, like "physical"
"Harming someone" is anything which causes harm. We have different words to describe different things. In this way, we can tell them apart when communicating with each other.