WTF dude. If they had a chemical weapons munitions carried on an aircraft then it’s very unlikely it dropped by accident. Is your post meant to be sarcasm?
Maybe just a couple of rogue Syrian helicopter pilots like the A6 crew in Flight of the Intruder?
Did you look at the pictures at the linked article. That is no "munition". It is an industrial gas cylinder, yellow for acetylene, like you'd get at any welding supply house - Praxair, Airgas, etc. - , still in its carrier. IF it got to where it is depicted through that hole in the ceiling then it did so because the rusty old carrier broke away from whatever it was mounted to. I say "IF" because this stinks of a Pallywood production and I wouldn't be a bit surprised to find out that the cylinder was hand-carried into a house that had a pre-existing hole in the roof and planted beneath the hole for photographic purposes.