So I just realized you missed a pretty significant secret on this level. In the bottom right corner of the pool room, there's a hidden switch. If you hit this, it'll open up a switch inside the short staircase at the top of the room. This second switch is too far away to toggle, but if you shoot a grenade at it, and then sprint back to the weird room with the Pattern Buffer, you'll find that one of the square platforms has dropped down. Step on it, and it'll raise you back up in a moment. Then, jump over to the closest platform.
You'll be teleported to a secret room on the far right side of the map, which contains two Shotguns, 13 Shotgun Shells, 4 AR Magazines, 4 AR Grenade clips, and a 2x Shield Canister. In the middle of this small room are some lights which spell out "EF", and at the bottom right of this room is a teleporter which will dump you back in front of the first terminal.
So the question is, what does "EF" stand for?