Huck and Jim initially start out on two different levels of the totem pole: with Huck, a young, white male being on the top; and Jim, an escape slave, being on the bottom. Huck understands this and thus treats Jim poorly (such as when he plays tricks on Jim or looks down upon him), but after their time spent together as runaways, Huck begins to understand and respect Jim— and even care for him.
This should be stereotyping because it would be implying that all people of that age, occupation, race, or similar, are the same and belong in the same group.
I would say that being anti-racist does not describe America after the abolition of slavery. For decades, up until maybe the 60's African American's were mistreated with things like Jim Crow Laws, that were stopped some time in 1964. While this had ended segregation it most definitely did not end racism. Even now hate groups, like the KKK, are very prominent in America, with over 1,000 recorded in 2018.
