Manning was a portly white comedian who was known for making jokes about blacks and Indians, using words that are commonly considered slurs. He was also known for making fun of dead celebrities.
So Knight is having a bit of fun making a joke about Manning being a "fat white bastard" - precisely the kind of joke that manning would have made about a dead black comedian.
It's funny.
Agreed, but here in the USA the humorous aspect would be irrelevant to the race pimps....if the person making the statement was white and if it was being directed at a black person.