Rednal
I believe what Khalid is referencing here is the idea that true "Islam" is "Submission to the Will of God" (or thereabouts). Ergo, those who follow God follow Islam, and in this sense the word should be considered distinct from the idea of Islam as a particular monotheistic religion largely practiced in the Middle Eastern/African/Asian area. Sort of how somebody can behave in a positive and "Godly" manner even if they're not Christian simply by doing good things.
Whether or not Islam is submission, is not my right to judge. However, I can honestly say that not all who are submissive to god, are followers of the Islamic faith. Using the two words interchangably would not be a good idea...