A “false flag attack” is not something any moslem would be ashamed of or horrified by if it served to advance Islam or one’s particular iteration of Islam.
It Islamists used the false flag before in Sarajevo. The story is that the US is actually complicit in this false flag attack, that the US trained the Islamists who were going into the region to set up a rebel capital and were surprised to find that the locals had switched sides, back to Assad because they were afraid of the outside radical Islamists who had taken over the rebel effort. They just wanted to retain control of their own territory, like they had under Assad.