If you look at the video (the file is actually smaller than the high-resolution still photo), you'll see that it happened very quickly. The spectators didn't have time to even recognize the impending crash, much less react to it.
The pilot had just taken off from the runway and started his first maneuver. He was supposed to complete it at low level, but didn't climb high enough to do so. When he realized he was going to impact the ground, he reportedly turned the plane enough so the impact would be away from the crowd, then punched out.