'sOK. I've been called "culturally Jewish". ![Psyduck :psyduck:](https://forums.questionablecontent.net/Smileys/qc/psyduck.gif)
Of course, that's considered both an ethnicity and a religion!
Alas, being culturally bankrupt, I'm but an Oyster.
More seriously, though, with a few exceptions, ethnicity and religion only go hand in hand, so far as I know, on the very small scale (The Sioux, to give an example. Even Judaism, the largest scale example of this I know of, only accounts for single percentages of populations, down to 1 or less, in most countries). For others, one is born in an ethnicity, but one (or one's parents, up to a certain point in one's life, at least) chooses one's religion these days. That being said, one can, as Cassius Clay (Muhammad Ali, for those not in the know) did,
alienate others of one's ethnicity by converting to certain religions*. That may be how Sidhekin's Tamil friend felt.
*Some may argue that Ali joined a new ethnicity (specifically Nation of Islam, or, more broadly, Black Muslims) by converting, but I'm not sure you can call it that. Something for cultural anthropologists and/or sociologists to quibble about, I suppose.