I'm not sure he even believes that there's an issue with American racism that's separate from economic inequality.

This is one of the things he is actually quite correct about. Identity politics is a ruse brought about by politicians who have a lot to gain from it, and it's bought into by large swathes of people who would be much better off focusing on how bad they're getting fucked every time they punch a clock. The reason the ghettos exist is because black people were systematically excluded from joining nice neighborhoods for many decades. Economics is everything, and every time we focus on what building is called by which name, or who made whom feel bad at the lunch table, all we do is take away from the much, much larger problem of lack of access to financial equality. Most modern racists (baby boomers, for example) are racist because they conflate race with welfare with societal morals. In the 2012 election, Rick Santorum actually came out and said what they all think, which is, "I don't want to give my money to black people." Money talks, and it's the only language everyone speaks. There's a lot of reason I don't care for Sanders' candidacy, but his insistence that racial issues are completely and totally entangled with economics is perhaps his most important message.