Ask a Muslim. They will say they are worshipping the God of their father Abraham. You can believe they are worshipping the moon if you want, but that's not what they believe.
I would agree they don't know Him, as they ascribe characteristics to Him that He does not have, and they believe He expects things that He does not and so on.
I don’t worship Abraham (a great Patriarch..sure), but I worship Abrahams’ Lord and God.