To be perfectly honest, this barely registered as offensive for me given the whole atrocity that is Cannoli, so I disagree that this is an especially loathsome statement from him.
That said, I don't know who uses "-ish" to describe someone's race. Ish to me implies an ambiguity and uncertainty about where something fits in a culture/race. Which fits the show perfectly, since that's what they're focussed on.
Saying that of a person who is unambiguously half-Black half-Indian is certainly weird, especially when we're reliving the painful trope of questioning her American citizenship.
Substitute half-Black in the sentence Cannoli wrote. Doesn't that read better?