That surprised me, too. But thinking about it, it makes sense.
I've said before that I think that black voters are probably the Democrats most cynical voting block. And after 7 years of Republicans obstructing hope and change with Obama, black people probably aren't going to fall in line with another Hope and Change candidate so easily. Keeping the white house is a defensive move here.
So you have Bernie Sanders, promising all sorts of fantastical things but remaining somewhat mum on the details. Lumping all criticism of his figures even by prominent and progressive economists as being part of the "Establishment" or, worse, paid off by Hillary. And swearing he's going to fight for black lives but not even bothering to fight for our vote.
I'm not surprised that some are starting to find him to be a bit dishonest.