It means she's not as bright as her position would have lead you to believe. It was a stupid thing to joke about in this age of political correctness, especially for someone in PR.
She tweeted that she was traveling to Africa. Said she hoped she didn't get AIDS. Just kidding, she said, I'm white.
That she's white and she doesn't have AIDS.
I am trying to figure out what PR stands for. I want to apply for her job.