The district in question has a black majority. He also used similar language with a similar district in Georgia. Plus with the Squad going 'back home' to their squalor, ****hole countries, etc.
Perhaps what's your missing is the narrative of majority black communities being inferior and not able to govern themselves. You'll see this trotted out about the crime and poverty in Baltimore, South Side Chicago, and other places. It's a well-worn white nationalist trope and was obvious in this case, to me at least.