I was walking home and someone caught me off guard and introduced themselves and told me he was a Muslim. I didn’t know how to respond and made a joke and kind of shrugged and said “Same G-d.” He laughed and I feel like maybe I said something wrong. I know Rav Avigdor Miller ztzl holds them as idolators so maybe I shouldn’t have said that. I wanted to know if this is a small or big aveirah. Thank you, Rabbi.
Although Islam is kefira, in the sense that they don’t believe the 13 principles of the Jewish faith, many poskim hold that Islam is not idolatry. In any case when you said that you were referring to those who hold that they do believe that Hashem created the world. Although it was a poor choice of a joke, in retrospect it doesn’t seem to be much of an issue.