Actually, it was 500 yards.
At 500 yards, an AR15 bullet (which is what he was firing) will hit you about 1.4 seconds BEFORE you ever hear it. What's more, from that distance and elevation, the sound will spread out so much that it will sound like it's coming from everywhere at once.
Nevada is an open carry state. The odds are that there were at least 100 armed people in that crowd. Probably a lot more than that, but I'm being very conservative.
It didn't matter. Nobody knew where the shots were coming from, nobody could tell, and when that happens you run like hell. A gun does you no good if you have no target.
It wasn't until quite a while after it was all over than anybody knew where the shots had come from.