Could well be. Smoke and carbon monoxide are denser than air, though, and in the environment of 1e, I would have the giants escape outside if at all possible.
It may be deemed a failure now, back in the day this was the first-place team. How "smart play" became equal to "bad play" I'll never know; but I suspect it had something to do with 2e and the rise of the "Plan out what will happen in your game session" meme.
RC
I don't know about being bad play, or 2E-ism design. I do know it's pretty easy to design a site made of wood (not a traditional dungeon, but realistic enough for the scene), and forget that the players could just set it on fire.
I had that happen in the 1st session of 1 campaign, and before they did it, I had to remind them that the BBEG supposdly had their crewmate in there. Otherwise, I very nearly had my simple short 1st adventure cut down dramatically.
I could have made the structure of stone to avoid that, but it seemed natural that it be of wood. I was just lucky that I could present the players with information that presented a Choice that would potentially discourage them from short-cutting my adventure dramatically.
I like the idea of setting up Situations, as thats what I try to do (and perhaps I misuse the word Plot when I describe it).
it may be, that as part of the design stage of an adventure, the GM check for:
chokepoints where if X doesn't happen the goal is stuck?
what if the PCs set it on fire?
what if the PCs go the wrong way, but think they are going the right way?
What if the PCs take too long?
What if the PCs fail at something?
I think if the PC deliberately go the wrong way (or don't bite the hook) or get hostile with non-enemies, the adventure you planned to run is done and you enter failure mode. Which is its own situation to deal with, and relatively a different topic/problem.