Looked it up, and,

Racialization or ethnicization is a sociological concept used to describe the intent and processes by which ethnic or racial identities are systematically constructed within a society.

OK. And the author said he was referring to the fact that society created race. Sure, fine.

I’m no less confused as to why one would refer to their friend as “racialized.” This friend is a person whose race has been created by society? But then that’s true of everyone. What makes the Dominican friend racialized if Karen is not? If they both are, why refer to one as racialized and not the other?