Since the very beginning Isis claimed responsibility for everything that happened. Because that's the best way for them to get publicity and put a scare into people. They want the world to believe that they are everywhere and can strike anytime etc etc.
When in reality they are trying fighting off attacks against their territory, slowly losing their grip on the middle east. They haven't been on the offensive in a long time. Because they're getting their shit handed to them on all fronts.