They're referring to being vegetarian, which is a Brahmin marker. To be more precise, while a vegetarian is not necessarily Brahmin, a meat eater is unlikely to be a (practising) Brahmin, similar to pork and Islam/Judaism.

> a meat eater is unlikely to be a (practising) Brahmin.

It’s not always the case though. The Bengali Brahmins or the Sarasvat Brahmins of Konkan are predominately meat eaters. It’s all mixed up.

Your accent will probably give you away. Or your last name. Or your physical features. Or they'll just guess you're a different caste and treat you differently anyways.