Guy was being a super asshole the whole round but as far as I could tell really was actually just trying to set up mix chamber for trit. Just wasn't being very safe about it i.e. working with pipes that were filled with hot mix gas and not completely disconnecting mix from distro.
What I'm guessing is what happened it's they probably accidentally connected a pipe from mix to distro while they were trying to connect it to waste, since that atmo area is super cramped.
Also fuck you, you don't have to have done stuff in sandbox to know how atmo works.