I just had the same "lockdown" in LAX Terminal 6 on Friday. They all came yelling out from everywhere, "NOBODY MOVE" "LOCKDOWN" etc. Very melodramatic. Still don't know what it was all about. Everyone was frozen for about 2 minutes ... if you moved you got yelled at. They were all freaking out talking on their walkie talkies until an "ALL CLEAR" was sounded.
It was quite surreal as if we had all become statues...