ISIS is full of people who believe the Mahdi is coming to rule the world, and that if they blow themselves up, they will get 70 virgin girls and many pedophilically described virgin boys to serve them in the afterlife.
I strongly suspect that you are right for once, Tyrion. ISIL maniacs believe stupid stuff like that.
The only thing I am not sure about is the Mahdi thing. You're mixing up ISIL with Hezbollah, which is kinda the same thing but even more maniacal.