I did not watch the video, and most likely will not (there are enough good apologetics against Islam that I don’t really need to look at the more far-fetched ones), but it is not so unusual that there may be cruciform symbols found in Islamic societies. If I recall correctly, Suha Rassam’s Christianity in Iraq (Gracewing Pub., 2006; now in its second printing) mentions something about a popular pastry in Oman (?), which the women who bake it make a cross-form across the top of the bread prior to putting it in the oven, but it is no longer remembered by them what this symbolism means. Rassam ties it to the early presence of the Church of the East throughout the Arabian peninsula, which did indeed once have CoE churches in Oman, Bahrain, Kuwait, etc.
I have also seen some photographs on flickr and other sites of buildings in Saudi Arabia which their uploaders claim are either understood to have once been churches, or are rumored (but heavily denied, of course) to have been such. While obviously the vast majority of KSA nationals and others of the region find even the idea that there once existed non-Islamic faithful and buildings in Arabia highly offensive and objectionable, it is not completely outside of the realm of possibility. Even the Qur’an records something of the legend of the (Christian) martyrs of Najran, which again Islamic sources show still hosted isolated Christian communities until about the 13th century. Of course, the modern KSA authorities do not allow any kind of research to be done in this area (people I know who have been to KSA say that you’re about as likely to be allowed to visit the area for research on Arabian Christianity as you would be to visit the Mecca on hajj as a non-Muslim, i.e., it’s absolutely forbidden).
While I do believe that Muhammad existed, a great deal of early Islamic history, including its relation to previous religions, is built on this kind of shrill denial and coverup, for lack of a better word for it.
