From this link, I read a passenger comment that made me scratch my head :
"The oxygen masks never came down and people began to freak out," D.J. Semenza told CNN. "The crew tried to keep calm and eventually called for an evacuation."
My thinking is that if you have smoke in the cabin, on the ground, that you'd not drop the oxygen masks since if you have a fire it might make it worse. (The masks do not seal against the face). Is my thinking correct? The oxygen masks are meant for a particular problem, which is lack of air to breath.
(I'll be happy to be educated/corrected if I misunderstand).