maybe a "sock" in one of the moisture seperators went bad or a Heat exchanger went bad or ECS pressurisation turbine
failure. I've seen such failures causing smoke in the cockpits of the aircraft types that I have worked.
"fire officials report..." is what the article said; fumes imply "unseen" (as opposed to smoke)...who knows, but I read that article that is being linked on this thread and now I wouldn't doubt anything.