I'd imagine that on that particular evening, Rosa looked tired and haggard, having worked all day and just wanting to be off her feet for a few minutes. She reflected the idea that true moments of courage can come about when you're not expecting them to.
Obama, in contrast, looks angry and pretentious in the photo, like he's just waiting for someone to start something with him. He looks, in short, like the self- absorbed phony that he is.