Whether or not something is considered racist is not dependent on where it came from. It's solely dependent on if those in power feel like it is racist. Remember the Pepe the frog meme? Pepe was a meme that got used by the alt right and now it's a "symbol of hate".
For the record I disagree with the sentiment but those are the rules.
There's an element of truth here. Part of the reason racial humor was so popular the first half of the twentieth century was because American leadership encouraged that zeitgeist. Granted, the "Censored 11" cartoons weren't direct propaganda (although some similar cartoons certainly were) -- but they and their audience participated in the cultural effect that is the desired extension of all propaganda campaigns. For example, the minstrel show wasn't by any means art or intellectual, yet its depictions were an extension of the claims about Africans by intellectuals at Southern universities, who in turn were currying to a leadership that was fully committed to keeping in subjection the "dangerous" African-American population.
For the record I disagree with the sentiment but those are the rules.