I think you need to open up a dictionary and see what the definition of terror is:
1.intense, sharp, overmastering fear:
to be frantic with terror.
2.an instance or cause of intense fear or anxiety; quality of causing terror:
to be a terror to evildoers.
3.any period of frightful violence or bloodshed likened to the Reign of Terror in France.
4.violence or threats of violence used for intimidation or coercion; terrorism.
I'm going to make a wild guess and say the people in Las Vegas were terrified.