"Gunmen spoke in English and tested hostages' knowledge of the Koran before allowing Muslim hostages to leave
No this couldn't be. The report must be wrong because the terrorists have nothing to do with Islam. Isn't that what some of the talking heads say? They are just extremists.
Some light reading http://www.theatlantic.com/magazine/archive/2015/03/what-isis-really-wants/384980/
The Islamic State, also known as the Islamic State of Iraq and al-Sham (ISIS), follows a distinctive variety of Islam whose beliefs about the path to the Day of Judgment matter to its strategy, and can help the West know its enemy and predict its behavior.
The reality is that the Islamic State is Islamic. Very Islamic. Yes, it has attracted psychopaths and adventure seekers, drawn largely from the disaffected populations of the Middle East and Europe. But the religion preached by its most ardent followers derives from coherent and even learned interpretations of Islam.