With two windows broken out the airflow would allow the shooter to keep breathing. Otherwise the gunpowder smoke, even with smokeless powder, would build up quickly.
I looked at some banners and other type flags in various videos during the shooting and while there wasn’t much of a breeze; there was some. Enough to clear the room allowing the shooter to keep breathing good air.
As prepared as this guy was; I bet he found a shed somewhere out in the desert (not hard to do) then started shooting hundreds of rounds from inside so the flash couldn’t easily be seen from outside just like in a hotel room. He probably found out the shed filled up with an acrid tasting, eye burning, smoke and fumes hence the two windows at different ends of the suite being broken out. The cross breeze was just enough even though it wasn’t much.
That’s my theory anyway.
Also, if you got to any indoor shooting range, one of the things easy to notice is the sound of big fans moving air through the range to move the smoke and fumes out quickly and away from the shooters on the line.
It would seem the logical thing to plan ahead for would be to get a couple portable fans and have them in the room to help keep the air moving around and somewhat clear. He couldn't really predict ahead of time if there would be any breeze that night or not.