After re-watching the video countless times, inc slowed down, I have concluded you are right and I was wrong.
That is a strobe. Further, after dozens of exchanges on Twitter, I am convinced that the windows do not open out, nor is the vent strip large enough for a gun.
There was no shooter that we can identify on floors 4-6.
Please add me to your ping list. At this point days later all we know is people are dead, that’s all.