It is correct because your point is a common dictionary point and has no practical application. There are hundreds of millions of Arab-speaking Muslims and very few Arab-speaking Christians. Furthermore, the vocabulary problem has nothing to do with clearing Greear because he does not mention that problem in his discussion. It is possible that Greear got his ideas from Vatican II in part although it is an old notion that religions all have a lot in common as even C.S. Lewis pointed out that this idea is not even superficial but just false.
Mohammad dictated a political and military system that touched off 1400 years of war. It is estimated that Islam has caused the deaths of 240,000,000 people. Islamic scholars admit to murdering 80,000,000 Hindus although India has no records. Mohammad called for world conquest by military force and conversion or death of all conquered peoples. So Mohammad/Allah have nothing on common with Christianity.