Yeah, it's not clear what her motivations were, based on the little seen. Could be religion, or, based on the "evolution kills black people", maybe some form of black nationalism or such. Whatever the "cause", the outburst does not reflect rational thought. As I said, I hope that she does get checked enough to see if there is something more to this. And if not, she needs to be reminded of the principles of civil discourse.
Regarding the filming, let's face it, with the ubiquity of phones with full video capability, any public outburst is going to get recorded, and probably stuck on YouTube. And while he could have asked them to stop, how effective would have that been, especially given his attention was monopolized by the young lady.