I know it's difficult for you to comprehend, but let me explain it in simple terms. The anti-government groups in Idlib province are known to have used poison gas weapons in the past. (This is according to the UN.) It's also a fact that a priority target for an airstrike would be a weapons cache. So the Syrian government targets a weapon cache, which just happens to contain chemical weapons, which then disperse and kill civilians. Rather than admit they had the chemical weapons, the terrorists claim that the Syrian government dropped them.

Plausible? Of course. In war you believe none of what you hear and only half of what you see with your own eyes.