That can’t be true. ISIS wouldn’t kill fellow Muslims, would they?
They have a rule of orthodoxy. Not enough in line with their ideology, you are expendable. Ask al Zawahiri. A man who does not embrace his own faith is an infidel.
One of the silver lining of this whole thing is that muslimes might wake up and see how evil Islam can be. Then hopefully they will reform it, just like most other religions/cults have done over the centuries.