So I think the float used the iconography of poverty to express the point of view that Obama is utterly lacking in achievement worthy of a presidential library. Maybe you could build an argument that because so many black people have been poor, any depiction of a black person as poor is intended to associate him with black people in general, and that is enough to warrant an accusation of racism. But I think this float belongs in the innocuous category of traditional American disrespect for authority figures.
Via Is depicting the “Obama Presidential Library” as an outhouse racist? @ Althouse.