Assad has absolutely nothing to gain that he isn't already winning on the battlefield. And the Russians would not approve of this, because these types of weapons are NOT effective, and are in fact more likely to turn people against you, especially after a week in which many western leaders admitted 'Assad doesn't have to go'. Calling it 'suspicious' is probably the best way to describe it, and previous chemical weapons attacks were shown to be either faked or originating in 'rebel' (bandit) territory, so the track record for credibility on these incidents is suspect at best. That the takfiri-bandits have chemical weapons is well known, and the Russians quickly commandeered the government's stockpiles back in 2013.