The article you mean is "Repressed Brits, evil Mexicans, Arab villains: why are Hollywood's animated movies full of racist stereotypes?" in The Guardian.
One example of the racial stereotyping is that the characters in the movie which are there for comic relief (so not given roles with a "serious" message) are voiced predominantly by black actors, which replicates the pattern of placing black characters in roles of providing amusement, but which are not treated seriously.
