I heard that the automatic weapons fire on the lower floor was actually a reflection or the light from an alarm, don’t know if that’s true or not.
If the Mandalay Bay hotel has windows that do not open, firing from the fourth or any other floor would leave a telltale show of broken windows. Other than the two broken on the 32nd floor, there have been no others reported.
You are correct.
What was in the lower floor video is the fire alarm strobe light, which is required now for hearing disabled people .
The strobe usually blinks quickly, pauses, then blinks again etc., when it is in alarm. The building fire alarm system was set off by the shooting.