True, but that's not really the best point anyways, because the idea people are pushing that all (or most) modern terrorists are Muslim seems like a very selective interpretation of modern history.
Prior to 9/11, you didn't find many people making the suggestion, because it would have sounded silly. Separatists in Spain, the IRA in Ireland, many different communist eastern European groups, militia idiots in the US, the list of non-Muslim terrorist type activity that's been around in our lifetimes goes on and on. Look at popular culture before 9/11, and you'll see a wide range of hypothetical terrorist bad guys, because at that point hardly anybody treated terrorism as a strictly Islamic thing.
Really, terrorism = Muslim is an idea that almost entirely rests on the events of 9/11 and the events around the follow-on invasion of two almost entirely Muslim countries. The insurgents/terrorists we found there, were people expecting Quakers?