White authors keep out

Two weeks ago in The Spectator Karen Yosman – Writers Blocked – reported a warning that white authors should keep away “from stories about people of colour.”

It was once my turn, as headmaster, to check the tickets of late arrivals for a school concert. A young man who had no ticket demanded admission and, when I shook my head he called me a racist and used his mobile phone to summon back up. I felt a tap on my shoulder. It was the head boy, a head taller than me and, like my protagonist black. “I’ll see to him, Sir,” was what he said and what he did, very gently, very persuasively.
Moments later, after the departure of my rescuer, a grandmother who was also black and had witnessed the incident offered to apologise to me on behalf of black people for the behaviour of the first boy. 
Moved by their kindness, how could I keep my white self out of this story?