Islam started in the Arab Peninsula, thus the first Muslims were originally ethnically Arabs. The religion of the Arabs at the time of the revelation of Islam was that of paganism and not of Hinduism. The origin of Islam and the Muslims had nothing to do with Hinduism, either as a religion or ethnicity.
The fact that Islam started between Arabs does not alter its universal message. The Quran stresses in a number of verses this global nature of the Islamic message. You may refer to the following verses in the Quran: "90:6" "1:25" "87:38" "28:34" .
confusion about the relationship between Islam and Hinduism is that when the Indian Peninsula was opened to Islam in the tenth century at the hands of the great Muslim conquers Spaktakin and His son Mahmoud of Ghuznah, most people converted to it. It is because this part of the world is heavily populated, a majority of Muslims now belong to this part of the world, which is the Indian Peninsula.