Well it's a massive flaw in their ideology.
Maybe it was just one sympathiser going there with a massive flag and no one underneath knew what it said. If a flag rolled itself out at the Amex I would lift it without knowing what was written on the topside. Just a theory of course.
We do know that there are lots of ISIS sympathisers in Turkey so I am not really surprised by this.
That said with regards to football, ISIS strictly forbids watching and playing it. So in theory, going by the principles of ISIS, anyone turning up to the game are infidels and should be...
After reading the article I understand the points made and it does look like we have forgotten the terror attacks in Turkey and Beirut and all the othew attrocities. If they were chanting Allahu Akbar I couldn't really hear it on the video. My first reaction was shock though.