Muslim Arabs were a large minority in Jerusalem during the Latin Kingdom and may have been equal in number to the Christian Arabs in the Kingdom overall. So claiming that the Muslim Arabs are newcomers to Palestine is just silly.
"The majority of the kingdom's inhabitants were native Christians, especially Greek and Syrian Orthodox, as well as Sunni and Shi'a Muslims. There were also a small number of Jews and Samaritans. The native Christians and Muslims, who were a marginalized lower class, tended to speak Greek and Arabic, while the crusaders spoke Latin, French, and other Western European languages."
Kingdom of Jerusalem - Wikipedia, the free encyclopedia