escaped
I think good teachers know not to overreact where name calling is concerned. Especially at primary level, because not all bullying is intended to hurt or be deliberate.
For example, some young children may see their behaviour as teasing the other child, like in a game. It's not malicious and although unacceptable, it can be quickly corrected without coming down hard. Often just a kind, simple correction can be more effective than punishment. The important thing is to change that behaviour for the future.
However, the problem is that this sort of low level intimidation can have a wearing impact on the targeted child, a bit like a relentless dripping tap over a period of time. That's why it needs to be corrected as soon as the teacher realises it isn't just an inadvertent slip of the tongue. Of course that takes experience or sharp detection skills which not all teachers have at their finger tips.
Involving police at age 9 for name calling does sound disproportionate to the poor conduct.
None of us knows the context to the OP. Of course, if this was just a 'one off' it's disproportionate to call the police (which I've already written). Nevertheless, if it's part of a wider pattern, it could be absolutely appropriate to call the police. I wasn't a primary school teacher. However, I was a secondary school teacher for many years and I witnessed a number of 11 year olds, whose bullying behaviour was already well-established but had been overlooked. The secondary school then had to deal with the results. Mercifully, it doesn't happen too often, but there are some young children whose behaviour is totally unacceptable and causes misery to many others. Jamie Bulger's murderers were only 10. Age and home background must never be used as an excuse.