Earlier quoted context omitted.
Racism is just shorthand for prejudices such as ethnocentrism, Orientalism, Othering.
I have never, never seen anti-Christianity been referred to as "racism" by anyone, not even evangelicals and fundamentalists. It would make large swaths of criticism of Christianity (not to mention many extreme metal bands) post-facto racist. "Othering" is far more general than racism, and relates to identity as a whole, not a specific racial identity.
However, one aspect that makes a difference is many Americans' picture of a Muslim is someone with vaguely brown skin. The people who engage in anti-Muslim hate crimes sometimes end up attacking Sikhs, non-Muslim Indians, even Coptic-Christians. https://www.splcenter.org/news/2011/03/29/anti-muslim-incide...
In a case where a culture conceptualized all and only White people as Christians and stereotyped or attacked them, I would see no problem calling that racism.