I’ve been telling people the exact same thing about WMD in Iraq and how it was moved into Syria just before hostilities.
One of the problems with weaponized smallpox is the difficulty in maintaining the usefulness of the weapon itself. Smallpox cannot live outside the human body for longer that a couple minutes before degrading to null — it becomes harmless.
After being stored in a hot desert area, I wonder how useful the remaining stock actually could be.
Storage under the right conditions and using a rapid dispersal method could make it very possible. I would be more concerned with spore bearing bacteria like anthrax or typhoid which could be dispersed through the water systems of some areas. There are a lot of vectors available.