The macacca is a type of monkey in India, I'm guessing that's the insult.
It's not a slur except for some Liberals who appear to have invented it.
A Macaca is a Macaque, a North African monkey that follows you around, begs for food, tries to get its hand in your pocket, tries to steal shiny objects, and generally makes a nuisance of itself.
Really, it was a very good description of this rat operative who was following him around videotaping him and trying to get something on him. Apparently his staff started calling him the macaque, and he went and used it in public.
Now, the establishment is on him because the kid is indian-american, i.e., dark-complected. As usual, they forget that according to their Prophet Darwin we are ALL monkeys.