Before the 60s "Palestinians" meant Jews. Since the 60s, Arabs decided to call themselves "Palestinians". Be curious, facts are very interesting!
"Palestine" is Judea renamed by Romans.
In 1798, philosopher Immanuel Kant referred to Jews as "Palestinians".
In 1936 a Palestinian Jew Franz Kraus created a famous poster to promote Jewish tourism to the Land of Israel, "Visit Palestine" was written on a poster.
There were many Jewish organizations like the Palestine Post, Palestine Electric Company, and the Palestine Symphony Orchestra. You can google and research everything!
In 1948 after establishment of Israel, Palestinian Jews started calling themselves Israelis. Arabs obviously called themselves Arabs and rejected the term "Palestinian" because it referred to Jews. So no one actually called themselves "Palestinians" from 1948 to 1964.
In 1964 genius Arafat and Soviet Russia decided that Arabs should start calling themselves "Palestinians"!
The purpose was to create impression as if Jews stole the land from Arabs (which obviously never happened). All this was to make the Arabs the "oppressed", because in the West it was already trending to support the "oppressed" and Arafat knew how to use trends.
More proofs and historical facts in the comments.
Note to fact-checkers: if these facts are not correct, I'll be more than happy to see your facts and proofs. And also, facts can't be Islamophobic or hateful.