How to respond in the rebuttal phase when the reviewer's concern is a blind review issue?
Ignore it.

Even if  your paper infringes the blind-review policy of the conference, it doesn't change the veracity of the results. It could, conceivably, have led to a desk reject without sending for review, but the editor clearly did not pick up on it, for he sent it for review anyway.

The reviewer's comment was as much a reminder to you as it was to the editor. Perhaps the editor should not have sent it for review, but since he already has, what's done cannot be undone. Just ignore it, and treat the rest of the comments.