1) The term Rohingya was not there in Arakan even before 1950s, roughly speaking. The term is quite related to Muslims there, and not before that.You are again saying existence of Muslim in 8th century. I said Rohingyas were not Muslim that time like entire south Asia. Rohingya history did not start with Islam. I think you have some comprehension issue.
2) Muslims from outside started to settle in Arakan throughout many Centuries that included Arab, Bengali, Persians and Afghans etc. Excerpts from an authentic edited article:
"Arabs were the earliest people to travel to the east by sea. The Arakanese first received the message of Islam from the ship wracked Arabs in 788 A.D. Such ship-wrecks occurred over and over in the coasts of Arakan and Chittagong.
This Arab presence, with the message of Islam, made up the nucleus of Muslim society in Arakan. Thus in Wesali the Arakanese practised Hinduism, Mahayanist form of Buddhism and Islam. The Burmese military regime affirmed in its official book Sasana Ronwas Htunzepho, published in 1997, “Islam spread and deeply rooted in Arakan since 8th century from where it further spread into interior Burma”. Meanwhile, “the Arab influence increased to such a large extent in Chittagong during mid 10th century AD that a small Muslim kingdom was established in this region, and the ruler of the kingdom was called Sultan. Possibly the area from the east bank of the Meghna River to the Naf was under this Sultan.”