I should add that I used a fast shutter speed — that makes for a very narrow focal distance. In other words, with a fast shutter speed, I can get Sarah’s face in focus, and the crowd behind her out of focus. I think that’s called “bokeh.”
It's not your shutter speed that affects depth of field, it's aperture. The camera adjusted aperture to compensate for fast shutter, lighting conditions and long lens which resulted in the photos you got. Now if you had your camera set for aperture priority, to adjust aperture to get better depth of field, the camera would adjust shutter speed accordingly.
Nice camera, but lots of settings to learn.