Well we also have examples like Avatar The Last Airbender. While it didn’t originate from Japan, many people still consider it an Anime because of its art style.
In my opinion, anime isn’t locked to Japan, it can be a worldwide thing. For example, consider how the Pokemon animes made it over to the USA. At least the American version is a truly American anime.
I haven’t watched The Boondocks, but their art style could very well be influenced by anime.