Unfortunately as far as Daesh is concerned the simple fact that those in the restaurant we not Muslims was all the justification they needed. And even if some were it still wouldn't have mattered to the shooters, to Daesh any Muslims who die in their attacks die as Martyrs for the greater glory of Allah (blessed is His name, or some such BS like that) and get a free pass to paradise.
The more I find out about Islam the more I am convinced that the world will never know any kind of lasting peace while ANY religions exist.