Commentary for Avodah Zarah 105:17

The Talmud now offers a different context for R. Hillel’s statement. Obviously, a Jew cannot annul the idol of a non-Jew. Why would the Mishnah need to state this? The answer is that the idol was owned jointly by both parties. The Mishnah teaches that while the Jew cannot annul the part owned by the non-Jew (this is obvious) the non-Jew can still annul his own part in the joint ownership.