If you watch the complete video the first burst is one continuous burst of way more than 30 rounds. Later you can hear two different guns being fired at the same time.
I thought they found live rounds, shell casings, magazines - even a pistol lying on the ground around the concert venue. Some victims had bullet wounds with horizontal trajectories, suggesting they weren’t shot by someone firing downwards from the Mandalay Bay. Whatever happened, they’re lying to us about it.