The Palestinian “Arabs” aren’t actually Arabs from Arabia. They are mostly indigenous populations living in Palestine who converted to Islam and the Arabic language after the Arab conquest in the 8th Century.
“Jews” are the part of the Southern Levantine population who kept their religion and language and mostly migrated elsewhere after the Roman conquest and the Arab conquest.
“Arabs” are the part who converted to Christianity and/or Islam and stayed in the Southern Levant, i.e. Palestine. While the Roman and Arab conquests resulted in some migration into Palestine, there was no wholesale replacement of the peasantry.
Jews and Arabs Share Recent Ancestry
https://www.science.org/content/article/jews-and-arabs-share-recent-ancestry
COLD SPRING HARBOR, NEW YORK—As fighting continues in the Middle East, a new genetic study shows that many Arabs and Jews are closely related. More than 70% of Jewish men and half of the Arab men whose DNA was studied inherited their Y chromosomes from the same paternal ancestors who lived in the region within the last few thousand years.
The results match historical accounts that some Moslem Arabs are descended from Christians and Jews who lived in the southern Levant, a region that includes Israel and the Sinai. They were descendants of a core population that lived in the area since prehistoric times. And in a recent study of 1371 men from around the world, geneticist Michael Hammer of the University of Arizona in Tucson found that the Y chromosome in Middle Eastern Arabs was almost indistinguishable from that of Jews.
Intrigued by the genetic similarities between the two populations, geneticist Ariella Oppenheim of Hebrew University in Jerusalem, who collaborated on the earlier study, focused on Arab and Jewish men. Her team examined the Y chromosomes of 119 Ashkenazi and Sephardic Jews and 143 Israeli and Palestinian Arabs. Many of the Jewish subjects were descended from ancestors who presumably originated in the Levant but dispersed throughout the world before returning to Israel in the past few generations; most of the Arab subjects could trace their ancestry to men who had lived in the region for centuries or longer. The Y chromosomes of many of the men had key segments of DNA that were so similar that they clustered into just three of many groups known as haplogroups. Other short segments of DNA called microsatellites were similar enough to reveal that the men must have had common ancestors within the past several thousand years. The study, reported here at a Human Origins and Disease conference, will appear in an upcoming issue of Human Genetics.
Yes, there were whole tribes of “Arabs” that originated as Christian or Jewish tribes who converted. And not just those living in Israel, but there were such tribes in Arabia proper at the time of the Muslim conquest.