'Bhai' is the Hindi/Urdu word for 'brother' and is used widely by South Asian teens as a friendly term of address for a male friend — similar to 'bro' or 'mate'. It has spread beyond South Asian communities online via Indian content creators and rap. 'Bhai, listen' is just 'mate, listen'. It is warm and informal, not religious or political. If your child uses it with non-South-Asian friends they are picking up multicultural youth slang, which is normal. No alarm needed; it is a mark of an internet-influenced friendship group.