Well, there’s only one God for all of us, but their representation or understanding of him certainly doesn’t seem to match up with how He’s revealed Himself, long before they showed up.
You are right there is only one “true” G_d for all of us, however, many choose to follow a false god and Islam is a great example of that idea. I personally believe that Islam is the anti religion, the religion given to the world to counter Christianity by satan himself ... complete with anti bible ... the Koran.