The Times referred to the Macpherson definition as an 'I think therefore I am a victim of racism' standard. But the merits of this particular case aside, it seems disingenuous to equate racial abuse with other playground bullying. This is not to condone other forms of bullying - teasing a child for being fat, for example, can sometimes be extremely nasty. They are just different. This may be obvious but it needs restating.
Racist words have a history.
They also have a worldview. Both the history and the worldview assume that the Paki, or whatever, is deeply inferior. They strike not just an individual but a tribe. Racial language speaks to deep wounds. To all concerned except the Asian boy and his family the incident must have seemed trivial.