The strobe light is irrelevant. In the taxi drivers video it is the sound pattern which confirms multiple shooters. One set of burst is a machine gun and much farther away, not just coming from another room. Long sustained bursts like that will melt a rifle barrel, so it has to be a machine gun like an M-60. Also these are much louder so that means it is quite far away. I'm guessing a machine gun nest was set up maybe couple hundred meters away, which is an easy range for an M-60, to pour fire into the concert area while the automatic rifle fire distracted.