The Palestinians were the people resident in Palestine. They are the indigenous people of Palestine. That is all. The reason the mandatory language is
"those who were habitually resident in Palestine" is because they were dissolving the Ottoman Empire, which had been the only political structure in Palestine for literally hundreds of years. But the people weren't Turkish. As genetics has proved, they are the descendents of Canaanites and Sea Peoples, Philistines, Assyrians and Jews, Romans, Arabians, Crusaders, many different migrations and influences. But there has always been a people present continuously on that land.
I think I will go with what a traveler to the area observed hundreds of years ago. After all, we have the prerogative to believe whatever we want to believe. Whatever, floats our boat.
A Tour and Census of Palestine Year 1695: No sign of Arabian names or Palestinians
A Tour and Census of Palestine Year 1695: No sign of Arabian names or Palestinians | Palestine-Israel Conflict