Some of them were ethnically Hellene. But folks of any ethnicity throughout the Roman empire (or earlier the Alexandrian empire etc.) of the time who wanted to do mathematical work would have probably traveled to Alexandria or Athens to study and would have written mathematical results in Greek, which was the language of science/mathematics/philosophy of the day.
We unfortunately don’t have too many biographical details about most of the famous “Greek” mathematicians, so it’s generally not precisely known what their background was.
We unfortunately don’t have too many biographical details about most of the famous “Greek” mathematicians, so it’s generally not precisely known what their background was.