The Swedish Equality Ombudsman says that racism "originally is a word that describes the division of people in a "race system"( like Apartheid) where certain races are biologically subordinated others. Today we talk more about culture racism - the notion that cultures are absolute, unchangeable and define the individual's characteristics."[2]
https://en.wikipedia.org/wiki/Cultural_racism
This actually supports my point.
There may be differences in biology or even preference in diet across many in the Islamic world, but what makes them part of one group actually defines a solidified, cultural state or identity. That cultural identity is their 'race', in which discriminating against same is simply racism.
It's really not that hard to understand.
In that sense, there's a Christian culture too. Christmas, Easter, commmon mores, etc. No different.
But not many Western Christians would identify their culture as just Christian. Only their religious culture, but not other aspects of their culture like language, food, etc.