One possibility could be they went into panic mode over some probably misc drone sightings due to supposed credible reports recently that ISIS was encouraging drone based attacks and that some of the original planners of drone based attacks in Syria are supposedly in the wind and possibly in Europe and they realised they had no way to deal with it and the repercussions if it had been a real attack under those circumstances would have been unavoidable.
Would explain the large amount of rifles on the scene.