I think it's about E R Braithwaite's outburst during an interview about his book. (He died at the age of I think 104 in Maryland, but was from British Guyana originally)
He felt that the film starring Sidney Poitier concentrated on the school (St George's Stepney) and not enough on his own life.
Also, some of the teachers who also taught there at the time were shocked at the false impressions given about the ethos of the school. They don't remember the lack of discipline or chaotic teaching methods that are described.
I'm interested, being a retired schoolteacher having taught in a very deprived area, and married to a black man who has his views on opportunity and attitudes towards black people here in UK.