I doubt there are 1,6B Muslims if the requirement is to recite an arbitrary verse from the Quran.
You can help yourself by learning some more about the basics of Islam. It will help you understand this situation better.
Al Fatiha is the Surah recited in every rakah (unit) of salat (prayer). Observant Muslims are required to learn it to have their prayers accepted. Minimum a practicing Muslim will recite it 20-40 times daily.
The story was only to show just how “Muslim” Daesh Khwarij Are.
The Daesh are recruited by people that use the Quran and other Islamic texts as reference and motivation. The Daesh believe they fight for Islam. That makes them Muslims in the eyes of the outsider. That other Muslims may disagree does not matter.
Ahmadiyyas also claim they are Muslims, and we reject them fully. Same for Baha’i and NOI, Moorish science, although they don’t take it so offensively.
The limits of faith are very important for any religious group as it identifies what is the proper Orthox practice and what is not.
For us, it is a necessity from everything from fiqh (judgements) , qanoon (law), rituals, and iman (faith.)
According to the main body of Islam, Council of Makkah, all Sunni, Shia, Ibadi Muslims are legitimate Muslims, and any other ideology is out of Islam. This is enforced by who is allowed to attend Hajj and Umrah in Makkah, and who is barred.
All Muslim groups are unanimous that Daesh are non-Muslims.
Ofcourse it suits the interests of some in Western governments, Western media, or some radicals in Non-Muslim countries to portray Daesh as normative Islamic behavior, which it is not.
It is a fringe group which has been rejected by every Muslim nation and every Muslim organization. They do not even have a single Faqih (Imam) which can judge in accordance with Islamic law.
Are you older than 15?
Some of us remember an era not so long ago when muslims blowing themselves up was unheard of. This is a new phenomenon spiraling out of control and it literally makes no sense....I'm still trying to figure it out.
Btw they've killed more Muslims than non-Muslims.
Taliban is actively hunting them down in Afghanistan, while US and ANA is functioning like their Uber, flying them from one province to another to prevent them from being defeated and becoming irrelevant.
In Syria and Iraq, the whole spectrum of Islamic movements under Turkey and Iran, from Sunni to Shia, are eliminating their remnants.