He is definitely not interested in any sort of religion. I usually say someone belongs to a religion if such a person accepts its tenets and practices its teachings. That would be the strict definition.
Then there are those who are so from family. Who are identified as belonging to that religion simply because they have parents from such a religion. They may practice something but may not accept its tenets. Can you call them as belonging to the religion? In a way yes. In a way no.
For instance my parents are Hindus. If some person wants to know which religion i belong to, in an official capacity i say i am 'Hindu'. At the personal level i don't consider myself a Hindu. Just as Christianity is based on the Bible, 'Hinduism' is based on 'Vedic Literature'. An umbrella term encompassing lots of books. While people and 99.9 percent 'Hindu' religious leaders use that term, in none of the books the word 'Hindu' is used. Its a word given by the people from the Arab countries. During the early medieval period the Indian subcontinent was under invasion by people from this area. India has a river to its North-West region named Indus.
Those who invaded the land did so from its North-Western side. From their viewpoint India is a country to the East of the Indus river.
Indus was earlier called 'Sindhu' river. They used to pronounce the river as 'Hindu' and the country to its East as 'Hindustan'. 'Stan' is a word meaning land. So 'Hindustan' was a word to indicate the land to the East of the Indus river and the people who live in this area were designated 'Hindu'.
So, i can't call myself Hindu. Its a name given by someone else while the word itself has no presence in the books themselves. It would be like saying i belong to 'Hudson' religion or 'Thames' religion.
At the same time i am more 'Hindu' then those who say they are 'Hindus'. I read those Vedic literatures. I cherish them and try to practice them. Religion in my opinion is a rubber stamp. A designation to divide people. I find all these religions in their core tenets are the same. There really is no 'Christianity' or 'Islam' or 'Buddhisim' and there definitely is no 'Hinduism'. They are all the same thing with each one focusing more on one aspect over the other. The leaders like Christ, Mohammed, Buddha and others essentially taught the same thing but under different circumstances to a different audience. So the differences are simply superficial.
Coming back to my family. My mother and father are both 'Hindus'. My mother has faith in many teachings of 'Hinduism' (Notice that i use brackets). She practices many teachings with faith. My father on the other hand does practice something but his faith is not as strong as the mother. Both are 'Hindus'. Yet i have faith which is based on reading and understanding the books while i try to practice them. I am not one. But in the eyes of society and even my parents i am one. A term which i consider meaningless and derogatory.
As you can see one's religion is a complicated subject. I did not know about Jewish. Assam gave a cool info that if the mother is Jewish the child is considered as Jewish too. So, it depends on how he is raised and how society sees him. Even then it would be more a designation. I don't think that on the personal level he calls himself Jewish. Unless some writer addresses this that is.