The keyword in that article is the word "killing." A bloodthirsty lot they were/are.
I'm reading a non-fiction book about Saudi Arabia the USA and oil. There is a section about a Russian arms merchant. He's pretty ruthless, worships at the alter of the almighty ruble, etc. Can acquire any weapon in any quantity. In other words not a real likable guy with real high standards (IMO). Even he describes the Wahabis as "wacky" and "ruthless". Wow, that was an eye opener.