No, they wanted the whole Philippines to be admitted to the Union. Now it does stick in my mind that this was after Black Jack Pershing's troops fought them for a while, and he impressed their leaders with both his ferocity and honesty, so the story of the change from .38 to .45 sidearms may be true as well.
Don't forget this was long ago: in 1918 there was still a Caliph, since Ataturk hadn't overthrown the Ottoman Sultan, Islam hadn't gotten its modern inferiority complex, and Saayed Qutb hadn't imported existentialist ideas into Islam (the intellectual basis of suicide bombing).
Back in the day, if you thrashed Muslims soundly, especially on the periphery of the Muslim world, they wanted to sign up with you (Queen Tamara of Georgia, who used to ride into battle at the head of her army, converted a lot of Muslim hill-tribes to Orthodox Christianity in the 12th century), and a deal where joining up with the victors let you keep Islam and get out from under folks who had been hassling you for centuries would have been very appealing.