You have to remember islam is way older than sikhism and has had time to spread, lets not also forget that some of the mughal kings as I said forced people to convert during their reign, so another reason as to why their are more. I am not saying that all were forcefully converted but a good number were, some stayed muslim some probably did come back to what they originally were.
Guru granth sahib is not a book to us. We do not worship it. It is a our teacher, our 11th and final guru. We do treat it like a "da-e thari" guru, which in your words like a human. In the olden days you bowed to your teachers, some cultures still do. Thats why we bow in front of it not because we worship it.
Just because you don't understand something doesn't mean its false.