They worship a demon, a false god that Yahweh warns His people to not fall into the worship of demons who manipulate the masses to worship them as a god.
You only worship the same God if they have the same characteristics. A trinity making Jesus God in the flesh is not the same description that the Quran uses. So by logic of non-contradiction they are opposed.
People can worship God's creation but fail to worship the true God. They may worship idols, demons, or false prophets but just because one worships, doesn't equate to it being the same being. The inward desire to worship may be evident of God as even the indians knew to worship something, but it doesn't mean the sun is Yahweh.