While I think that you can talk about having acceptances and other interviews if asked specifically, I wouldn't answer this question saying that.
This question certainly is asked because many people don't get into med school. They want to see if people are realistic and have thought about other options.
More than that, I think it is a time to explore other interests and an additional chance to emphasize what you like about being a physician. You can say that you would do another job for reasons x, y, z. If those can also apply to medicine, I think that is a good thing and you can make that connection.
Just saying, "I already have an acceptance" is kind of a cop out imo, and I don't really think it addresses the intention of the question.