He might not have been the first black Metropolitan police officer. There's an argument that Robert Branford in the 19th century might have been. But it's not certain. And either way, Norwell was still a trailblazer worthy of attention and praise.
As expected, the poor guy received a ton of racial abuse. The fact that he persevered through that to become a Detective Sergeant shows his ability, intelligence, maturity, and grit. He's a fucking legend.