This old thing. It is wrong and has always been wrong. Quoth:
"Race is a social concept used to categorize humans into large and distinct populations or groups by anatomical, cultural, ethnic, genetic, geographical, historical, linguistic, religious, and/or social affiliation. First used to refer to speakers of a common language and then to denote national affiliations, in the 17th century, people began to use the term to relate to observable physical (i.e. phenotypical) traits." [0]
But more importantly, they are an ethnoreligious group, defined by shared ethnicity and religion. [1]
So, not all Jews are Jews, and not all Jews are Jews. But the classification is not always religious.
"Race is a social concept used to categorize humans into large and distinct populations or groups by anatomical, cultural, ethnic, genetic, geographical, historical, linguistic, religious, and/or social affiliation. First used to refer to speakers of a common language and then to denote national affiliations, in the 17th century, people began to use the term to relate to observable physical (i.e. phenotypical) traits." [0]
But more importantly, they are an ethnoreligious group, defined by shared ethnicity and religion. [1]
So, not all Jews are Jews, and not all Jews are Jews. But the classification is not always religious.
[0] http://en.m.wikipedia.org/wiki/Race_(human_classification)
[1] http://en.m.wikipedia.org/wiki/Ethnoreligious_group