Based on the information in the article, the following items would have been required to stage something like this:
- Foreknowledge of the bombing by the Syrian/Russian coalition, including time and place.
- A high probability that there would be many people suffering from hypoxia following the bombing.
- False canisters ready to be deployed to the area.
While not wholly impossible, it does seem unlikely to me, and as such I believe that the headline is a bit of a stretch.
I think it would be more accurate to focus on OPCW and they way it compiles and presents it's findings.