I think your confusion results from the fact that "Palestinians" was the name used to call the Jews basically for nearly two thousand years, until the early 20th century. And, yes, they have been ethnically cleansed by arabs basically since the arab invasion in the 7th century.

The arabs themselves never wanted to be called Palestinians - they used the name "Syrian Arabs". Yassir Arafat, former leader of the PLO, was one of the most prominent opponents of the word "Palestinians" with regard to the arab population - he only changed his mind as Jordan and Egypt signed a peace treaty with Israel, because he wanted to distance himself from these "traitors".

One of the problems he (and also most arabs) had with the word "Palestina" - it has exactly ZERO relationship to arabs and to Arabic languages. It's a greek word with actually Hebrew roots. It means "land of the Philistines" - and the Philistines, according to many historians, are a mixed group of people, mostly from western Mediterranean (modern-day Italy, France, Spain, northern Africa), also called "the sea people", or, in other words - pirates. The Romans introduced this name to the region to wipe out the original names Judea and Samaria (which IS actually a sign of a genocide).