Britain abolished slavery when Dickens was 21, so he hadn’t been much of a crusader for abolition. He didn’t like American slavery, but that wasn’t unusual for someone coming from a country that had already abolished slavery. His opinions on the US were also affected by his disputes with American publishers over copyrights. Dickens was quite chauvinistic and bloodthirsty in supporting British repression of rebellions in Jamaica and India, so he’s probably not somebody I’d cite as an anti-racist or a reliable judge of what was going on in the world.
Of course, nobody has cited Dickens as an “antiracist”. That particular grift did not come along until the last 10 years. To try to imply that he had some kind of anti-American bias is simply laughable. He came to America on speaking tours multiple times. He was clearly an abolitionist and an outspoken one at that. Yes, he expressed those views in the South (so much for claims that nobody dared express such thoughts or they’d be beaten to a pulp for doing so in the South) before the war. His antislavery views were well known. He just didn’t buy the false claims of Northerners made years after they started the war that they were doing so to end slavery. He could see their nakedly financial interests in wanting to keep control over the Southern states.