Those displaced was because of war to other parts of Palestine. How many Jews were left in Gaza or the West Bank, or East Jerusalem for that matter in 1949, or the rest of the Middle East after Israel became an independent State?
I will repeat for the readers: UNRWA definition of a Palestine refugee in 1952: “A Palestine refugee is [a person] whose normal residence was Palestine for a [minimum period of two years] preceding the outbreak of the conflict in 1948 and who, as a result of this conflict has lost both his home and his means of livelihood.” –In the 1948 General Assembly proposal included all stateless persons who had been residents of Palestine for a minimum of two years.