That’s what they’ve been taught to call Israel: “Palestine.” They’ve also been brainwashed to believe that Israel is responsible for their poor economy and many other problems.
When they say Palestine they mean the Arabs. They might call it the Zionist entity or something similar if they meant Israel.
For them to shout, “Death to Palestine” means that they are opposed to continuing to support the terrorist entity that many are trying to carve out of Judea and Samaria (the so-called “West Bank”).