Depending on the size and programming. It should all flash at once but I have seen a lot that looked out of sync. In the case.of this it looks like one room from what I saw. Like someone was testing the room. Also could be ice cream delivery alert system.

Of course I say this as a 16yr Master Electrician that has specialized in Fire Alarm systems for the last 10. So, checked it again and it is definately an alarm strobe. Might not be part of the fire system(a lot of these are also used for other alarm systems.) But it is definately not explosions.