ISIS doesn’t have a habit of claiming one that wasn’t theirs. IOW, so far, when they claim it, it turns out it’s theirs.
“The group has a history of exaggerated, unsubstantiated or false claims, but these have picked up in frequency as its position at home became more tenuous.”
http://www.chicagotribune.com/news/nationworld/ct-islamic-state-fake-claims-20171005-story.html