Taking a long view, the headline is almost certainly true, as the police were complicit.
But the deadliest attack in Turkish history wasn't the one mentioned in the article, but one of the mass slaughters of Armenians and other Christians during the genocide largely carried out by marching Armenian, Assyrians and Greeks into the desert and letting bandits attack them. I'm sure one of those bandit raids on a "resettlement" caravan claimed more victims than the Daesh killed in 2016.