Not quite what I meant. I would hope that you agree that Catholics do not worship the same God as Muslims do.
Well. Muslims profess to worship the God of Saint Abraham, and the God of Mother Mary, Who is the True God. So it is a little more complicated than that. If they formally reject Christ, then yes, they worship a false god. If they are in inculpable ignorance, and are worshipping God as best they can in the situation (e.g. if they live in a place where there are as yet no Christian Missionaries, or very few), then it is a different situation, as even the Pope Saint Pius X's Catechism admits. All the docuмent says is that Muslims profess to worship One God, the God of Abraham.