Islamophobia is a type of racism. Brown people who aren't even muslim (like Sikhs) often get caught up in it, precisely because the ignorance that fuels it is based in racism.
So we argue that “Islamophobia is rooted in racism and is a type of racism that targets expressions of Muslimness or perceived Muslimness”
The reason it seems "muddled" to you is likely because bigotry itself is based in ignorance.
Many people just accept and absorb what they've heard or seen in cartoons and popular media while growing up, lumping different groups of people together based on oversimplifications and misrepresentations of who they are. The assumptions on which people base their Islamophobia are quite racist, conflating Arab identity (which people think they know by a person's appearance based on racist stereotypes) with Islam. The point is to be able to identify the bigotry for what it is.
If you try to define a form bigotry by the actual reality it's misrepresenting, you'll miss the bigotry itself.