Some white people appear to think that non-white people have a strong ethnic or racial identity by default. They may think that if a non-white person is unaware of her race or ethnicity, it is a result of white interference. However, ethnic and racial identities are socially constructed, not genetically inherited.
Infants of colour, for example, are born without knowing their race, their ethnicity, their culture, or their history. These things are learned. Learning culture may involve learning skills, learning history may involve learning knowledge, but learning racial and ethnic identity often involves the internalization of social categories of difference and otherness.
Perhaps white adults have a weak sense ethnic and racial identity—if they have any at all—because they have not had the same experiences with being othered and being different.