If they were heading to Sinai, they wouldn't be killing Infidels. Sinai is controlled by Egypt, and Egypt has no love for ISIS or for the Muslim Brotherhood <-- Obama's favorite group. My experience says they would fighting other Muslims with ISIS for control of the peninsula. Hamas is there. The PLO is there. The Muslim Brotherhood is there. Iran and Hezbollah have agents there. Egypt is there. And they are all fighting each other for control of territory in Sinai.
These guys may have thought they were going to kill 'Infidels', but no. They would have wound up in the middle of a fight between various terrorist groups and Egypt.