if he said something about how much he enjoys chitlins and watermelon, then goes off into a "rap" routine for a bit, and peppers his prepared speech about tax reduction with words like "slammin'" or "wack." "I want to restore the principles that made America the powerhouse of the Earth, yo."
What has happened, I think, is that Mittens' handlers have realized that he has absolutely no idea how to communicate with people outside his little circle of filthy rich Mormons and hedge fund managers, so they've told him to pick up on some aspect of the location or culture of his audience. Like, "OK, Mitt, today you'll be speaking to a group of Nebraska farmers. Say something about corn so it looks like you're interested in what they do." But unfortunately Mitt is so tone-deaf from years of isolation in his rich-guy bubble that he is unable to comment on some unfamiliar topic, like corn, in a way that conveys the impression that he can relate to the audience or that he gives a shit about them.
When he speaks to an African-American audience he will feel the need to establish some kind of connection with them, but he doesn't know anything about AA culture other than the stereotypes he's picked up from his rich Republican friends - so whatever comes out of his mouth in his sorry attempt to "connect" is likely to be lame at best, racist at worst, and certainly cringe-inducing.