They are khawarij worst than kaafir, they believe sin makes you kaafir therefore being worst than a kafir by altering God lawAlshabab are not Muslims because they believe in their hearts that tens of millions of pious Muslims are kuffar. This belief renders them kafirs.
If you believe that something that is haram, like killing 800 Muslims, is actually halal & that you will get ajr for it, you are a kafir.