Conference reviews contains the whole range of ratings
This happened to me twice. I think the rebuttal is only necessary for the rejections (1 + 2), or the weak accept? the strong accept requires no rebuttal. It's hard when there's no extensive comments. But when I did my rebuttal, I just targeted my response by reviewers (as in, I wrote separate rebuttals for each, and labeled them as such). If there's not enough comments to go on, can you write to the conference organizer asking them to solicit a bit more info? once I received a blank comment page, but as it turns out the reviewer made a PDF of his/her comments and it failed to attach. Not saying this is your case, but it doesn't hurt to ask.