If I hit yes, I'm tagging friends who might not want to be tagged. Furthermore, I might end up in the same boat with friends tagging pictures of me! Either way, I help better Facebook's facial recognition, which unnerves me.
On the surface, clicking "no" means that they got the facial recognition wrong. But what am else am I revealing? If the match was 98%, would they infer that one of us (or both) is concerned about privacy? That we have something to hide?
The third alternative is to click nothing. The only information that gives Facebook is that I'm not interested in helping curate their data any more than I already am.